like starting a music school, bob?
some good models, believe it or not, are preschool models. (laugh if you must). they establish good payment policies, attendance policies, cleanliness ideals posted everywhere (when students should not come - if sick - guidelines), rules for employees to keep pianos clean thereby avoiding student sickness. ie malvern pre-school
also, because some are a franchise- they do not have to literally start the business from ground zero. much better to have someone else paying for the building and initial set-up. also, they send you all the papers of how to get started, right?
bob, if i were to start a 'group piano' class - i'd just invest in a bunch of smaller electronic pianos and move with the times. kids enjoy that just as much as acoustic. i realize i am probably going to upset people - but hey, you don't know if children are serious until the second or third year. why not move up after a couple of group classes to just become familiar with the keyboard and the basic stuff.
have one grand piano - but lots of electronic pianos. in fact, maybe even teach how to play them by reading through the manuals and getting familiar with the potentials of electronic keyboards. after all - this could open up many doors to composition. if i had a school - i'd have group piano, group composition, and group piano performance or master class (on the one grand).