Consulting an attorney is your best bet but attorneys have different opinions of prop 215 and how to interpret it so I think there's not just one exact correct way to start a collective and they do not have to be incorporated. Co-ops on the other hand do have to be incorporated according to the a.t. guidelines.
IMO, most of these MMJ attorneys are land sharks. Not to dissuade anyone from consulting an attorney, but well reasoned and good info to make one's decisions can be found by anyone willing to read the many discussions from everyone here on this site.