The graphite is applied by adding it to epoxy. I would prefer an epoxy fill coat applied over an epoxy coat rather than have some varnish in between. Also I would varnish the top of the graphite to protect the epoxy from uv rays. It may contain black graphite and offer excellent UV protection to underlying layers but I would worry about the actual epoxy containing the graphite.

It would be a simple solution to use graphite in fill coats during construction to build up the protective layers that you are looking for in a graphite hull. IMHO Adding a layer of varnish is really pretty easy as long as you are emotionally prepared for the scratches but it may be overkill. P.S. Dont forget the silica or you will have a slick soft hull rather than a slick hard hull and that would be a hull of a thing to forget.

Robert, Visionary