Having been in flying groups over the years i believe books are a good start but chats with engineers at the airfield where you intend to be based are essential.Spamcans may be bland but if you intend starting a group with the minimum of risk then consider a C152 or C172 no new group member wants grief because the aircraft is grounded through lack of parts availability or maintainance costs.Cowboys exist in aviation engineering companies just as they exist in the motor trade so teaming up with a terrible engineering company maintaining an unusual aircraft may start off being ok but end up costing you loads of money and stress.Keep an open mind because for example at Shoreham on the south coast at the moment it is so competitive and cheap to hire an aircraft from a flying club that to invest a large sum in a group share is not worthwhile.