If you are going into this with no experience selling used cars and working at a lot, you should get in touch with your state used car dealers association. They can provide you with everything you need to know, the forms, etc.

While having an on-site repair facility and quick lube operation may seem like a good idea, how many combined operations like this are you aware of? Marketing a quick lube is an ongoing business, weekly newspaper coupons, etc. which will require some of your time. Keeping the shop full will be a requirement, so you can afford to pay the techs, again time away from the used car business.

While there are some repair shops that sell used cars on the side, there are few car lots that also promote service, since it is an entire "full time" business that will have you wearing a number of hats.