The steps and how many times those steps are repeated depend greatly upon the condition of the vehicle. With 2 coats of epoxy and 3 coats of high build, you have a good bit of material on the car. Did you block sand the car with 180 using a long board or did you just sand it to scuff it up? What color epoxy and high build did you use? It would be helpful if you used different colors becasue this will let you know when to stop sanding. Regardless of how straight you think the body work is right now, I would use a guide coat to point out your low spots and sand with 180 until I hit epoxy. If your guidecoat is pretty much gone at this point, you know you're work is straight, and it is just a matter of stepping through the grits to refine the scratches from there. If you have trouble sanding off your guide coat in some areas, without sanding through in ohters, you will need to repeat the process or use filler, depending how bad those areas are.
Remember to use an "X" pattern when blocking and only push with enough pressure to hold the block against the car without flexing the panels. Don't increase your sanding grit until the guidecoat is sanding off evenly.
