3v3? Shouldn't you adjust accordingly to how many members sign up? It'd suck to have only 4 teams or something.
Also, wouldn't approximate level be kinda stupid? People will have leveled, some more than others, depending on how much they play/their level.
Some PvP team balance may be needed too. Do you really want a group of level 40's vs a group of level 25's? The 40's have most of their vital skills, while the 25's have a pocketful.
Prizes never hurt either...