I would suggest planning another $3-5K in up front costs for a few extra rental/loaner scooters. If someone brings in a warranty repair that's gonna take you a week or two to complete, or you get in a bind, suck it up and provide a free "loaner". As you get better at the service work, you'll be lending out scooters far less often, but while you're learning the ropes, the loaner bikes will buy you a ton of good will.
In the early 70's Subaru had just started selling cars in rural Pennsylvania. They were cheap so my dad and I went to look. The dealership was very small, and was a 2-3 man family operation at best. The shop owner was tied up w/ contractors installing his drop ceiling, but he greeted us warmly. "Is there a specific car you guys are interested in?" My dad said "The 4wd wagon." The dealer grabbed a set of keys and magnetic plate and handed them to us. "You can test drive that one if you want. If you come back in about an hour, I'll have time to talk to you." We drove that car all around and got a pretty good feel for it w/o high pressure sales. We came back to the dealership and my dad bought one. About a year later, the car needed some minor adjustment to the fuel system. We took the car in and pretty much got the same treatment. "I'm not sure when my mechanic can get to it. Probably within the week. If you leave it, you can borrow a demo off the lot until it's ready." I think he had our car for about 2 weeks, but how could we complain? He'd given us one to use in the meantime. My dad bought 2-3 cars from that dealership over the years, and the dealership grew... until Subaru went upscale/corporate and started behaving like every other dealer. He lost his franchise to a bigger multi-line outfit.
Also, if I were opening a scooter shop, I'd think hard about carrying Honda clone bikes like the Skyteam Dax, Z125, PBR, etc. They're pretty nice and very easy to work on. I've also found pit bikes w/ that "Honda Monkey" style engine to be very tough. They could probably be sold for around a grand and still make you some profit. With a little practice an engine swap can be done in under an hr. Parts are very cheap too. Carbs for $30-$40, CDI boxes for under $10, etc.
Good luck and have fun !
Couple Airhead BMWs
Couple Chinese Pitbikes