Does anyone know what influences the teamwork stat? I assume it has something to do with the leaders stats, but is it a stat like intelligence, potential... or is it something like a combination of stats among the team members? Like if one member has really low dance, or if the main vocal has too high dance and too low vocal, that sort of thing?

The concepts seem somewhat random compared to the actual songs and I'm pretty sure the labeling is wrong on some, or that the intended outfits don't exist in the game. For example, some songs I've systematically tried every single outfit choice under that label with the correct accessories and can only get 2 stars max. So here's what I do: I buy every outfit set under that label and try each one, obviously with corresponding accessories (it doesn't seem like the extra tags you mention apply to accessories, but I try to correlate them anyways, ex. sneakers and short socks for a sporty look but not for a preppy look). Usually after you release a record you get a few concert invites that month to test out new outfits. If you manage to figure out the right outfit, then use that one for the actual concert. You can also guess sometimes based on the concept of the actual song (google the name and look for the music video if they have one or translated lyrics) whether something should be school themed or not.