Not sure about the quick fair question. This is from their web site regarding epoxy resins:
"Can I put polyester gelcoat over cured epoxy?
In general, polyester resins won't cure properly or bond well to epoxy resin products without a "tie-coat" barrier resin in between. System Three SB-112 resin system can be used as a tie coat in between epoxy laminating or coating resins, and polyester laminating or gelcoat resins. Using this resin allows you to gelcoat an epoxy-built or epoxy-repaired boat. "
as far as the blisters go I would do like you are doing, However be careful how much you grind out. It just makes it that much harder to fix and fair later on. I don't envy you during this stage of the game.
strick