Well it seems 3 is the magic number, as its 3 home town members required as well. I think someone should be able to own more than one town, if there are decent arguments for only owning 2 towns id be happy to give up one of mine. Personally, regardless of my situation 3 just makes more sense to me. Also as the owner can only be the home town member of one, he/she would need an extra recruit in his/her other towns for the gen to turn on.
I dont feel that the size of the town should affect the number of home town members needed because to increase the size you must have built in most the protected area. Therefore if 3 people can build a giant town, let them, they will have enough trouble balancing gathering money to run the gen, and building. It would therefore be in their interest to recruit more players anyway but don't force them to.