I don't have any experience in renting out bikes or working in a bike shop, but wanted to wish you best of luck. Sounds like you know what you are getting into, and you realize you will not make the same money. But money is not everything, how many times have you heard I've never been more broke or more happy in my life.
You don't have your'e location filled in, where are you located? Where is the shop going to be? Maybe if I ever get out you're way I'll need to rent a bike.