I RO sanded the epoxy with 60 then 100 grit, then wet sanded by hand with 100 grit. The wet sanding seemed to be the best way of washing off the epoxy sanding dust that sticks in spite of dry wiping. The varnish (I used Z-Spar Captain's) fills and hides the sctatches.

I wet sanded between varnish coats with 220 grit. The varnish clogs dry sandpaper and its good to geet rid of all than sanding dust outside with water during the varnishing operation.

By the way, a cabinet scraper is without doubt the best tool to remove epoxy drips and runs and to feather build ups at tape edges. It is too easy to power sand through the cloth adjacent to the thichened areas. Scraping goes quickest with only 24 hours of epoxy cure.

Take a look at http://www.greenval.com/FAQvarnishing.html