IO has some good points, but they apply more to ownership and small groups. Your plan of 'non-equity' shares and tiime builders captures the least caring and most cost driven part of the market.
So they will not look after it, they might 'flog' the log, they certainly will not operate the engine so it reaches tbo, clean it, worry if it gets scuffed about...
So the sort of costs people are giving you can be factored up by almost any amount. The group I was in many years ago had 2 'time builders' out of 20 members. Virtually every dispute and every technical glitch came as a direct result of them.
Bluntly it was not worth the blood pressure so we gave them the money for their shares and chucked them out - peace and tranquility returned...
From having to ask these questions you obviously do not have the experience of running an aircraft - that can be difficult enough, adding in 19 others who in most cases will not give a damn? A mugs game I'm afraid.