Congrats on a great plan!!
If you haven't already, talk to the people at http://www.flatsquirrelscooters.com
on Randall Rd. in Algonquin / Lake in the Hills. Very similar demographics to Naperville. They've been around for a few years and will certainly know a little about the market.
I like your idea of rental, Americans in general don't know the joys of scootering and rentals will be a good way to get them into it (remember your first experience). I'd also find a way to market to the younger crowd, certainly to the college kids and even to high schoolers. In the Naperville demo, many kids have their own cars. You'll need to make a scooter 'cool'. Maybe a promo tie in with the high school or college??
Here in Crystal Lake, we have started to see a few scooter gangs -- groups of high schoolers riding around -- very good to see and they are clearly having a blast.
Regarding the comments on getting an upscale brand -- I fully agree that you will need to offer a known brand. Scooters are a tough niche -- between cool and can't afford a car. In Indiana, they are known as the only means of transportation for those with a DUI -- not the image you want in Naperville.
Kymco may be a good start, but I would not go with an unknown. You might be able to fill in that niche with a few used Vespas or even Hondas. Given the upscale nature of your market, you customer will certainly want a strong brand image, and will be willing (and able) to pay for it.
Best of luck -- always good to see a new venture!