Epoxy primer question

I used Southern Polyurethanes Epoxy Primer and I really liked it. Spayed nice and sanded nice. But I've never used any other epoxy primer so nothing to compare it to.

SPI claims a 7 day recoat window without scuffing. But since the overlap areas will be minimal, I would scuff it anyway. No problem with your approach.

If you spray two wet coats of epoxy, you'll be able to scuff your epoxy with 80 grit before applying filler without going through to metal.

I sprayed epoxy again over top of my filler and then used a primer surface that was a different color. That allowed me to see when I was about to sand into my filler or through to bare metal.