Treat it just like you would sheetmetal. Are you using a spray gun or rattle can?
If it is spray gun, talk to your supplier. Sikkins, DuPont and the other major one(I can't remember the brand name) all have many different kinds of primer. I wouldn't worry about using a filler/primer.
If you are using rattle cans, again stick with a name brand, like Krylon. Really, any primer should work.
The key will be in the prep work. Be sure the wheels are clean and oil free. There is a cleaner ( I can't remember what it is called either) that painters use with a cheese cloth to remove oil and particles from paint surfaces. Clean the wheel, prime it, let it cure for 24 hrs, wet sand it with 600 grit paper, clean it again, then paint.
Aa far as the part inside of the tire, I would clean it and prime it, then leave it at that stage. Get a good coat and call it good.