Finish the primer with 600-800 (I use 800 personally but it's not always needed) and then spray your base and follow up with correct flash time and lay on the clear. If you get trash in the base, wet sand it, spray your color on that spot and continue to the clearing. If I am painting over a vehicle that has it's original paint or may have spots on it that I am not sure will cover or cause problems with the base then I will highly reduce SPI Epoxy primer (acts as a sealer) and put on a very light sealer coat, let it dry for about an hour and then proceed with the base coat.
Good luck!