I guess you have some mods installed... So you already know this. But if not - here you go:

0. Choose, which one do you want to get - full PolyRoms, or just a party component.
1. Download and install ME3Tweaks and Community Patch for LE3 (both links are present in the "requirements")
2. Use "ModManager Download" button in the "files" on this page
3. Import mod to the library after it is downloaded
4. Install it from the library. 
Yay, you did it!

Glad you asked!
There are several blocks of stuff my mod provides:

0. Basic
Well, it is a mandatory part and the sceleton of mod itself. It allows you to have several romances instead of one, deletes some checks on commentaries from your squadmates and makes other basic setup running. With only this mod option on, you will feel like you have got a bunch of romances, and everybody knows about practically every partner you have. Get all the romances experience you can have!

Options
All of these options can be found in the in-game menu (upload/start/etc game, press pause, look at the upper button in options wheel. Here it is, feel free to use!)

The good thing in in-game menu is ability to change settings at any moment of the game without any issues. 
I recommend  toggling jealousy, quietness, other romances permissions and "extended party" once when you begin your run, and have fun with other settings. But you can do it any way possible, the chance of wrecking the game by toggles is pretty low.

Warning, chosen settings are stored in game save files, so you will need to set up configuration you want to have at the beginning of every new run! You can easily change it later, but until you do it, game will run with default settings (all yes-no toggles set to no, no one chosen as a "party hookup" or "true love", and Liara is on the couch)

Romances settings

 No jealousy
There is jealousy even in poly-relationship, it is natural to be, so i didn't remove it mandatory, if it didn't break ability to begin romances. But if you hate the very idea of jealousy - here is the option removing as much of it as i could! Also i removed all the catfights with this option.

• You can still provoke jealous dialog by yourself, so the ability to smash Jacob's face is NOT a bug.
  

If i missed any jealous lines - you can report about it in a "romantic lines" bug report topic, and i will either think about removing it in future updates, or explain, why is this line kept.

Quiet romances
Do you feel like you don't want the rest of your team know who you are romancing? This option will remove alny side mentions of your romances your crew makes (well... almost), and will remove (almost) all flirty lines coming from your love interests any other squadmates can hear. 
Avilable only if you turn "No jealousy' option on!

• This option doesn't affect some references to ME1 and ME2 romances - they are REALLY needed somewhere, so it seemed logical to leave them.
  For example - if Jack romance references from her scenes in Gryssom were removed, it would be unable to proceed with her romance afterwards. But i made a short-cut in that dialogue, so it won't feel too revealing.
• James will always be aware of your romance with Cortez. He just can't be NOT aware. He heard almost every dialog you have with Steve in cargo, and Cortez apartment scene in Citadel DLC requires James to know, so - yeah, he just knows about this particular romance anyway.
• Also this doesn't remove the ability for you to show your feelings by yourself - so you can still kiss Traynor in Citadel DLC, and so on.
  

I used my own subjective looks to figure out, which lines are needed to be removed and which are not! So if you are using this option and found something, that is not quiet enough for you, or i missed anything - you can report about it in a "romantic lines" bug report topic, and i will either think about removing it in future updates, or explain, why is this line kept.

Choose your "True Love" option
This setting allows you to choose, which one of your partners will be there for you in culmination scene in the endgame, who will you wake up with after the party, and who will be there for you in a "goodbye" scene after the party (that's why Thane is also an option).
If the game needs information, which one of your squadmates is your love interest, and "a bunch" is not an answer, this option will let it know.
And - it is also able to affect the choice of the squadmate, who will come to resque you in Citadel DLC. (If your "true love" choice is on board of the Normandy at the beginning of DLC - they will come to save you! Just ensure you pick person you wanted to see there before the restaurant!)

Mod provides these priority romance options:
Garrus, Tali, Liara, Ashley, Kaidan, Traynor, Cortez, Jack, Miranda, Thane... Or none. Just don't choose anyone. By the way, "none" is default, so check dettings before getting true love moments, otherwise you will get lonely Shepard.
(For example, "none" option can be used intentionally, if you want to see Joker's goodbye scene after the party)
I highly reccomend not to choose the person you are not going to or not able to romance. It is just pointless, you know :)

Tali/Garrus romance option
If you want to see these two have relationship, no matter if you romance anyone of them or not, this is your option to pick!
This option is dedicated to ones who love "Shalibrations" relationship (thanks to Audemus for the name :))

James/Ashley flirt option
If you want to see these two flirting, no matter if you romance Ashley or not, this is your option to pick!
This doesn't work, if you choose not-light hookup with James, so you need to decide, if it will be Ashley or your femShepard involved in flirt :)

Party settings (party settings together form stand-alone party improvements mod, that can be used without PRM)

Party hookup option
This setting works for femShepard only, and it allows your Shepard to wake up with James of Javik after the party, overriding the true love setting without any need to re-choose true love.

You can either take full James option, or pick a light one, there is description below, telling where is the difference.

• The full Lames option requires some conditions to be made besides turning option on:
  

1) Turn James option on before one-on-one meeting with him in apartment. 
2) Do the vanilla stuff you need to do usually to wake up with James: flirt with him both when the meeting with him is going on, and also on (rowdy) party

• The light James option does only require to choose it before party ends and run the rowdy party. You just end party, wake up - and boom, here is James nearby.
  

If you wanna see his wakeup and skip all the flirty-hunt stuff going before - this option is for you! 

As for Javik - just hit that button and run rowdy!
My mod completely overrides OFM feature for Javik, as if you use a manual button to decide if you want to experience his wakeup, i think there is no need in mission/relationship count checks added on top of it.

Couch neighbourhood 
Select who do you want to see near you on the group photo! It is detached from love interests now and can be regulated with a button! Share couch with anyone you like! The ony non-avilable options now are Joker and EDI (who are already on the couch), and also krogan - they are way too big to fit on a couch like human-alike squadmates. 

If you don't work with this setting, you will get Liara next to you on the couch.

Expanded party
Don't want to choose between rowdy and quiet party? Well, don't! this setting will loop party, so you will have:
Phase 1 - Quiet phase 2 - Quiet phase 3 - Rowdy phase 2 - Rowdy phase 3.
Together these sets will allow yo to experience the most full party avilable without any save-loads included

Right now this mod is compatible with:

Take Earth Back
Expanded Galaxy Mod (the invites and the photo will work with true love. Wanna change? Swap the setting! If it didn't help - keep settings the way you want them to, leave the floor and then come back)
More Gay Romances
Optional Flirting Mod (James not-light hookup option will only work if you flirted with him trough the entire game)
Choose Your Friend (the choice you make with CYF will always override my mod, also person who came to save you will act friendly and not flirty, if this mod is on, before the rest of your crew comes to apartment)
Padme's cabin additions and memorials 
Easy Pull-up Competition mod

Also mod has an in-built compatibility for Community Patch LE3 and definetely compatible with Multiple Romances for LE2 (it was obvious, but i still need to mention it), so you can import your polysexual Shepard from LE2 and not experience any trouble!

If you are not sure mod is compatible with mine - ask, i will make a check!

This mod is definetely NOT compatible and not going to become compatible soon:
With Starchild-be-gone. Well... Not exactly INCOMPATIBLE.
You can install it, romance trigger (the reason of problems) will work correctly. But if there will be mods released that allow you to get someone else at the cabin before HQ (like Miranda or Jack) - you won't be able to get to them: if you romance Cortez, you will get Cortez instead. If it doesn't bother you - well, no trouble, use these mods together. If you don't want to risk - disable setting for dream#3 while installing SBG, another dreams work fine.

I wanna more patches! I found mod/i have a mod in need of patch to be compatible with yours.
Great, then let's make more patches - i love compatibility!
If you want to use my mod with any other mod you are not sure it is compatible with - ask me, i will check it up, tell you results and maybe create a patch, if needed!
If you create or already have any mod, that can conflict with mine - inform me that you are making a patch (no approvement needed, just tell me and go working) and/or ask me to develop one!

Not automatically. And there are several reasons why:
1) (tech one) the end of each single scene triggers the next plot phase. Too problematic to edit.
2) (plot one) There is a little time both after party and before Cerberus attack. It is illogical to have several scenes in this case - there is no time for it.
3) (is it needed? - one)The wakeups on party are pretty the same exept one or two voice-lines, coming from partners, and i don't think it is actually needed to experience them all at once - you will be tired of the repeating sound samples and content very soon, if these scenes are running in a row. 
And as for culminations - you can easily launch several scenes one after one with minimum effort put in, and that's why.
The game makes a "legendary save" automatically before you trigger the Cerberus attack, so you can:
- upload this save via "load the game" after the previous culmination is done and game allows you to enter pause menu
- switch the true love choice in mod settings after (!) the load is complete
- trigger the attack again and see another culmination
Easy-peasy, you won't even need to close the game! :)
Be careful - there is no culmination for Thane (for obvious reasons), Jack and Miranda in vanilla. My mod doesn't add them either.
Don't meet the final mission alone until you don't want to, check up settings before you start, so there is reachable true love nearby!

Nope. You still need to follow the romance rules to be able to romance the ones you want to - be nice, not dump them and so on. 
Also this mod doesn't add ability to ignore your gender in romances! 
If you play as femShep and want to romance Jack or Miranda - there is a More Gay Romances existing. Also there is a femShep/Tali mod for LE3 in progress, and i will work on a patch once it comes out. If there will be any more romance mods for LE3 - i will check up ability to patch too!

Well... Yes and no. 

• Text localization: there is english (INT), german (DEU) (no party), spanish (ESN) (no party), italian (ITA) and russian (RUS) text existing right now. The others are automatically replaced by english, unless there will be a translation.
  

There are two text changes i made for one dialog wheel (chat with Thane in Huerta before the Coup). Also there is the in-game menu. It is a little amount of text, so, i think, it is toleratable even in non-translated condition, so don't be scared, it won't make game difficult or uncomfy!

• Sound localization: Mod is fully localized for english sound. As for the others - the very basic setups are not dependent of language, so you will definetely get an ability to have most of the romanses. Also true love option will mostly work okay (But true love option won't work for Thane, and you will get automatical true-loved Cortez, if his romance is activated. Somehow.). The "no jealousy" setting will also work (not completely though - several glimpses will remain.)
  

The problem is I did not only modify language-independent content. I also did a big work removing any small issues from english localised files - like refusals of some characters (like Allers) to have romance, if you have any another romances, automatic priorities of choosing, who is going to say romantic stuff, if it is a crowded scene... And the whole quiet option is running on the localized dialog edits, too. It is not critical, but it can be not so great to experience, so it is up to you to decide if you want to use this mod in non-english raw version.

Definetely not, if i am doing it myself. No. For both text and voice.

• As for text - i am not able to translate text into languages i don't know. If there were single words only - maybe, but not the complete sentenses, not the instructions. If you want to offer your help with translation to language which is not covered yet - feel free to contact me, i will happily give you file to translate and help, if it is needed!
• As for sound - i have suffered enough with the english one, and i don't feel ready to repeat this three more times. But if you have skills in sequence and dialog editing and want to offer your help with localization - i will gladly agree. Contact me, if you want to offer your help!
  Well, ma-a-a-ybe, one day i will begin working on it by myself... But it won't happen any time soon.

Mount 9998 (9997 for Party improvements)
Added conditionals 25353-25361
Added plot Integers 12479, 12480
Added plot booleans 31500-31520
Added tlk id-s 9896498-9896575 (PI included here)
Overwritten tlk id-s 639083, 639084

If you need more info, contact me