Mark, the general idea is to have enough layers of epoxy so that when you sand the surface in preparation for varnish you don't cut into the glass. You are sanding off the high spots to the degree that there are no high spots, if you put on a lot of fill coats there could be everything from bugs to mountains of drips to scrape/sand off, if you put on a minimal thickness of fill coats the weave of the glass may be showing through with just enough filled into the low spots that careful sanding brings it all to one layer. So you could start with 80-150 grit and end with 150-220 grit depending on how things are going and the nature of the shape. hey, I'm a rank beginner compared to some of the folks here so don't take anything I say for gospel. It takes a while to figure how much is too much and what's just right,,,and even then there's still room for error.