Becoming a oil, fuel, prep sales source (at track or internet) is going to mean a rather large outlay of money to be able to compete on price.
Randy Ransom (ATTL) asked me many years ago why I don't sell Trac Tac, and I simply answered that every other kart shop already does -- I'd be competing on price alone. That's not something I want to get into. To compete on price, you must be able to purchase a TON of product and sell that same Ton every 30 days. Now, we DO sell a good bit of his product, but we don't even try to compete with the distributors on pricing.
Any products that we make here in house, anything that has our labor invested into it, becomes considerably more valuable as we are the only ones that the product can be purchased from, (Carlson Racing Engines, Vector Chassis, Vector Cutz Blueprinted Tires, Vector Tire Preps, Vector Clutch Rebuilding Services, etc.) When the product is the exact same thing that everyone else already sells online - you fall victim to competing on price alone -- and that lessens margins considerably. Then there's the IRS and state tax id, business license, etc. Don't think that the government won't take a share (and then some,) and don't think they'll make your upstart business any easier.
If you're just wanting to start out with something as a "hobby" business just to get your feet wet and learn the ropes...just pick up a prep brand and retail it locally at your track. If you're connected with someone already - work with that person. Run it like a lemon-aid stand and keep it below $600 to fly under the radar until you're ready to get serious about starting your own business. That's not my legal advice, btw. You've got school and helping around the house/shop to fill your time too, remember.