For best results you need the shop to be self supportive. If the shop can stand on its own then that is great, you don't want to have to rely on the track to keep you afloat. If you can can it to work that way they your 100% better off.
The more stuff your shop has in it the more chances you have to sell. The more overall hobbyshop you have that sells other stuff than just r/c cars helps. Trains, models, AFX type slot cars, paints and other crafts all will bring in a wider list patrons to your shop.
Some of the better shops also have a great website to buy products from and good promotion of this site to help drum up business.
Food at the track is kinda to fold. Its great to buy from the shop but it is an extra expense to have a full state approved kitchen setup. The shop I work out has this but it was expensive and also you need yet another employee to pay for serving food on race days. If you just sell food from a crock pot like hotdogs and burgers sooner or later you will have problems from the state since its not approved. I watched this happen to more than one shop so I would be prepare either to get the right stuff or just pass on the food. Just have a soda machine and sell that along with snack type foods.
Money making margins are small in industry and honestly most shops buy from the same few distributors (Horizon, Great Planes, HRS and a few others.) Also alot of places you need to order direct so lots of time on the phone ordering.
Parts is where you make money as kits in general have smaller mark ups.
This is just alittle info I know from working at the shop I work at and many of the things the owner has gone over with me. He is a personal friend before he had a shop so I get a lot more insight that most do.