I have my car in epoxy primer, before laying down base should I spray a high build primer over and sand smooth, or should I sand epoxy with 320 then spray base on top?
You are on step 1, with epoxy primer. Epoxy is simply a metal sealer, to prevent corrosion. It is waterproof and the best way to protect bare metal.
Now I would recommend sanding it with 400, and shoot it with a 2K primer. Then do your body work on top of that. When you are satisfied with your body work, sand it with 320 and shoot the entire car with Feather Fill G2. At this point you have a decision to make... You can shoot your base over the Feather Fill, but be prepared to lay down a couple of extra coats. The FF will soak some up.
Or, sand the FF with 400 and shoot the car with a sealer. Then you can lay your base coat down on top of the sealer.
Paint jobs are not a quick in and out thing. Lots of steps involved.
