Once I lay the fiberglass how many coats of epoxy do I need to apply? And do I need to sand between each coat?
The first coat squeegeed in place wets the fiberglass and the weave is prominent. By the third coat of epoxy, rolled on with a foam roller you will start so see the weave disappear. The fourth coat should be relatively smooth. Obviously if you sand between coats, this will affect the fill rate. You should adhere (pun intended) to the manufacturer's directions, but there are a lot of variables with regards to sanding. Blush/non-blush, chemical bond vs. mechanical tooth, curing rates and times between coats, etc.
With all that being said, I actually used the weave as part of my non-skid in my bright interior...