To be honest I don't think these questions warrant a new topic but meh.
1. Yes but you need to unlock them first
2. Only a select few songs can be used for quintets
3. Yes,it's trios only.
4. No, quartets're not in the game because NBGI is too lazy; I think it's because they don't really have a way to spread 4 characters in 5 slots and make it symmetric without making a new choreography for a song..
Although for the quintets, they have to make some quite rapid changes for the songs (Honey Heartbeat in duo or Solo is the most obvious of examples - there's no 'lead' in that song anymore, so certain things don't happen)
It's mostly more effort than it's worth in most cases - it'd be making another quintet subcatergory, and since at the moment only 5 songs even support quintet out of the current 19 (The world is all one, Megare, im@s 2nd mix, Smokey Thrill, Honey Heartbeat) although I swear there's a 6th out there.
You'd have to decide where they are, what they do. It's pretty intensive work planning then executing. Would they eventually? Possibly I guess, if they think it'd sell.
My brain needs to wake up though.
To note, you can guest in a quintet in story mode with a certain type of event and all quintets are limited to 4 stages at this point in time. Otherwise the information here's accurate.
