Well....I apply my epoxy with a brush...a pretty good one actually. I scrape with a carbide scraper between coats. The final...or near final coat...I scrape and sand with 80 grit paper. If the finish is fair and looks GOOD ENOUGH for me...I then sand with 100 grit sandpaper. If the epoxy finish doesn't look fair and good enough I apply another coat, scrape, and start the sanding process again. After sanding with 100 grit I varnish using a VERY good brush(in the $15 or $20 dollar range). About using your boat for a short time before you varnish...I do. In fact you need to wait until the epoxy is hard (cured well) before you start sanding. I almost always use the boat for awhile before applying the final coat of epoxy and sanding for the varnish. I've never had any problems this way...though I have heard others caution about it. I use my boats pretty hard