The people are what really matters. No amount of contracts can get around that.
The members need to be compatible in
- mission profile (if a group is some-VFR and some-IFR, it will fall apart when some avionics packs up and the VFR ones don't want to pay for fixing it)
- funding (a stingy member will not want to pay his share)
- flying frequency (there is no way to structure the /month and /flying-hour figures so there is never a cross-subsidy from frequent flyers to infrequent flyers, or vice versa, so if there is a big disparity in patterns, resentment will result)
One also needs clear rules on things like duty drawback, otherwise you will get 1 or 2 members always flying over to LTQ and pocketing the drawback. The drawbacks should go back to the group fund, but that is not perfect accounting either...