[TommiTheTaco]

"invite people to attack with you, they have a couple mins, choose yes or no, and they're either in or not."

Wouldn't be a good idea if you need to get someone in a rush. Waiting for people to agree to attack with you would leave them too much time to attack all of you in return.

Another reason why I chose the group of 3 people thing. If any of those people're in the same district as you, they will automatically join in the attack, much like a real gang would do. Prevents the whole gang from being in the same fight and ruining the rosters.