Epoxy primer is not intended to be block sanded. You can wet sand it with 400-600 wet to knock down any dust in it.

Your plan sounds pretty reasonable, and sounds like you have some previous experience. If I was doing a down and dirty paint job on that car, I would sand it down with 320 and a DA. You really need to ensure all the areas where the clear is worn or delaminated is removed back to a solid substrate. Fix any dents etc with plastic filler or glazing putty depending on depth, or your care level. You really need a 2k primer surface to cover any body work you do. Finish that out to 320 dry. At that point you can epoxy prime the entire car. If you go with black epoxy, you can run that as a satin finish itself. While not being a topcoat, it might save you some effort and cash for your timeline. If you want to finish with the hot rod black, you can shoot the epoxy and let it flash off then shoot the topcoat over it. Your choice since it will all be masked anyway.