As you fair any glass/epoxy, there's going to be feathering that's necessary along shear taping. coamings etc. where you will be forced to sand into glass. I usually go at my first round of sanding any lumps and fairing tape with a ROS and 60 or 80 disc.

As I wash off the boat with soap and water, I am left with an immediate proof of how the glass will wet out or if it won't (show fibers). Areas that won't wet out well or are showing fibers, I hit with 220 wet sanding. Right before you eyes you will see the troublesome areas disappear as the water will suddenly wet the fibers out. You need to do this even if you are planning another fill coat of epoxy.

Wether you need another fill coat or not is a tricky queation. If glass is showing everywhere, you should fill. If only your tape fairing areas are showing and a few small areas, you could go to varnish. (this is opinion here.) the boat won't be less or more strong in either case.

I bring my boats down to a 220 wet sanding before I apply my first coat of varnish. The important thing is that the fine wet sanding will make areas that wont" wet out or where weave is showing - wet out transparent.