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Your original post indicated you want to restore the bottom. Not sure how old this boat is.

The purpose of the epoxy barrier coat is to protect the fiberglass & gel coat on the bottom from water intrusion over time. To get a uniform seal of the barrier coat you'd want to be certain you have sanded surface (approx. 120 grit) for the epoxy to adhere to the gel coat. Thus sanding / blasting will deliver that surface. You would not want the epoxy to be adhering to antifouling. If the barrier coat areas are in good shape, I don't see any problem in coating over it, assuming the new barrier coat adheres.

The purpose of the antifouling to is prevent organisms growing on the bottom, (obviously). it doesn't prevent water intrusion.

You mentioned a number of dings, etc in your hull. I'd imagine if you removed all your bottom paint, you would see a lot more dings than you would see from removing some of it. That said, the existing barrier coat probably has some dings.

I'm finding my hull is a labor intense job, and includes a lot of sand, fill, sand, etc., etc., etc. to get the hull in nice condition. I've patched / filled every ding , screw hole, and hardware mount hole. I am ready to barrier coat. Now just waiting a good weather window to do it (outside). I've resigned myself that the boat probably won't make it back in the water this season.