I'd say teams are allowed (Im not going to cap the size) but if your project wins.. umm.. i guess you'll have to rock-paper-scissors for who gets the free game copy, because there's only one of those going. I'm not going to put a limit on team size.
There are categories in Overall, Gameplay, Visuals, Audio, and Theme Adherence.
And I have no clue how many people are going to join the jam, to be totally frank. I've never done this before. It probably won't be many though.