Pointers to Setting up MU site for franchisees

I’ve set up my WPMU site and the way I’m envisaging ot working is a client signs up and gets their own domain area.maindomain.com which has some pre-installed plugins on it and the theme etc. One of the plugins must be a booking system for which their OWN clients may register as well. Any pointers as to best plugins for the different registrations, events etc