I play in GIGCB a band consisting of about fifteen musicians.I say about because with that number of musicians rarely all can make it,one band member living in Germany,one in Spain and another going backwards and forwards to Brittany and others doing many other things other than full time committment.It is great for most of the time,some gigs I would pay money to be in the group and of course I do, because we rarely get much for attending, split between all the members.One person needs to be in charge.Organisation is a major factor and as we are all busy then this can break down on occassions.
Remember that although you get on great just meeting for one nights playing a tour or a week long festival can be very stressful.
Starting a band requires agreement on the type of music you intend to play, agreement on the tunes and a flexible attitude to new tunes being introduced.
Al