Paint questions...

The epoxy primer is a direct to metal product. You can bondo over it without going back to bare metal. I scuff it up, but it doesn't sand very well unless it has been on for awhile. I agree with the 2k sand etc. but if you are going with a lighter metallic color,silver, blue gold.... finish with at least 600 wet.I agree with alleyoop and red that you get what you pay for with the products.If money is an issue I would use the better quality basecoat, and use a mid tier clear. 3-4 coats of clear max.
I work in a PPG store so you know what I would suggest. We have a real nice mid-tier clear jc630, that air dries quickly and buffs like a dream..
My 2cts

Bob