When it comes to getting a group together, try and keep it small- around 4 people- give or take. If the group is too large it can become unmanageable and complete chaos. Their needs to be trust; you don't want to send clients someone's way if they'll never give you anything in return. I know some photographers who will have a contract, stating who pays whom what. In my opinion that's up to you. The most important aspect besides the trust, is to lay out a mutual agreement, on who gets which job. You can try just going in rotation, or keeping track on who received what.
So what are you waiting for? Do you have your network?