My experience with the topic... hope you continue using car paint as well.
1 if you cant sand blast the frame just use a steel wool to etch it really good so the primer gets a lot of surface to stick really well.
2 use your favorite car primer, the nice about epoxy primer is that covers really well. Since I paint in my backyard i use u-pol high surface primer that is a car professional grade rattle can primer, awesome stuff. Never a single issue with this thing not even peeling on the dropouts that is the usual problem in any paint job.
3 use car paint, since your friend knows about this i wont give you any tip because the paint will come up as good as the painter and the paint is. I have used cheap ass paint and stuff like dupont, nason and sickens for example.
4 clear coat... the clear coat has to be sanded and shot depending on the paint instructions, some paints you have to clear after like 30 mins or 3 hours, with others you can wait 12 hours to do it. In the case you want to clear next day always you can sand with 600 grit wet sand paper and shot the clear over it. I always used 3 coats or 4 because I sand the clear a lot to get rid off of imperfections in the surface and then a super nice polishing.
IMO the results in the finishing will depend of the clear itself and in the how much you sanded and polished the clear coat.
Some clears are really bad and other ones no matter how bad the paint is (if primer is good) the clear will be as hard as a rock and will protect the base color just like in a car; that's the reason I use nason clear coat, If the clear was shot wrongly or the wrong clear coat was used then the rocks and junk will get to the paint and the paint job will nick really easy.
Somebody mentioned about UV protection curing???? 1st time i heard about UV curing.... If the clear doesnt have UV protection the clear will turn yellow after a few months, rattle can clear coat like rustoleum doesnt have UV protection (they have one that does now) and in quality is not neither even close to the hardness of polyurethane clear coats. Rustoleum paint and clear is just junk for a descent and durable bicycle paint job.
The day somebody shows me a paint job like this using rustoleum i might change my mind about that paint.
