My experience with Epiphanes in particular is in repair - specifically, one of Mr. Walker's guitars. More on that later.
Re: Mr. Walker's finishing schedule: a note to him with a bit of background and a few complements sprinkled in between your questions would not go amiss in soliciting his advice.
Generally, small shop and site-work spar (long oil) and medium oil varnishes are brushed, as they self level quite nicely with either an excellent badger-hair brush ($$$$) or a seemingly cheap, genuine PolyFoam disposable brush ($). Further - because they need anywhere from 3 (so-called quick-drying short-oil varnishes with accelerators) to 12 hours (phenolic/tung spar varnishes) to dry to be dust-free/able to handle, spraying does not provide the advantages seen with lacquer or even waterbased finishing.
When the Walker job came in, my mentor and generally gruff PITA occasional shop-mate handed me a copy of Ms. Rebecca Wittman's book, Brightwork - The Art of Finishing Wood, directed me to read it over the intervening week, then be prepared to discuss and execute the repair. Tucked under the dustcover flap was a collection of correspondence with Ms. Wittman re: restoration of the varnish work and teak decks of Mr. Stock's 37' cutter-rigged sailboat, with her unvarnished
admonitions and some critical assessments of products that later made their way into Ms. Wittman's follow-on book effort for International Marine. Fascinating stuff. Besides that note to Mr. Walker, a used copy of Brightwork in paperback might be worth the $20 or so US dollars... I see some copies on Amazon. Most of the advice in the book is circa 1990, judged largely still valid as of 2021, and is stated from Ms. Wittman's POV informed through decades of operating a commercial marine finishing business in New England (US epicenter of traditional wooden boat building and use... although Seattle is apparently close behind). My repair work on the headstock of the Walker took about six weeks end-to-end, with two weeks of cure time (varnish is a curing finish versus lacquer or shellac - both drying finishes), and was undetectable via the usual clues (texture... witness makes, etc.).
A few thoughts from someone with rather limited experience with the material: phenolic/tung oil varnish is rather picky about associations. It really, really likes clean, well-sanded wood and other clean, well-prepared varnished surfaces. Oil-based pore fillers work, as well as wet-oil sanding to create a slurry to fill grain, but can be quit muddy-looking on some timbers. Eschewing a fill stage and building from one or two well thinned sealer coats might work, as might a Silvertip epoxy fill (the boys have done this on a few projects, although not on any instrument to date that I know of). As mentioned earlier, a note to Mr. Walker might be the best info available re: duplicating his finishes.
Good luck, and IMO, you are off to a nice start on at least the joinery end of things. If you have a hard time finding a copy of Ms. Wittmann's book, PM me and I will see if I can liberate it from the confines of the Greenridge shop library for a brief spin to the northern shoreline of Lake Ontario.
