You could do worse than look at the Guide to Varnishing over at the Classic and Vintage Dinghy Association, as we can get a little bit competitive over varnishing.
My 100 year old full sized rebuild project has about 24 coats (lost count!) on the hull, though they are thin coats and I flatten back with 240 wet and dry every 3 or 4 coats. The deck still needs the final coats added, but I’m waiting for consistent temperature and drier air. I always use a foam roller and tip off with a genuine Jenny brush.
I use a traditional varnish (International Schooner) as my only varnish as I can touch up any wear during the season. I’ve used pretty much everything over the last 30 years, I don’t get on with Epifanes. If I’m varnishing carbon fibre for UV protection I’ve had excellent results with Hempel Diamond, but doesn’t have any give in it so I don’t use it on wooden boats.
I only use the recommended thinners and use a base coat for all varnishing, used to use UCP before it was banned but now use a Clear Epoxy Penetrating Sealer as a primer then apply the first coat just before the CPES has fully cured as this bonds the varnish into the timber.
Don’t need to go to so much trouble with models but I start with a few coats 50:50 thinned then gradually knock back the percentage of thinners, I never use an unthinned coat, even the last coats have 5+% thinners.
I spent 20 years with a converted cow shed as a workshop, with no heating so i was used to varnishing and painting in less than ideal conditions, probably why I stick to using Schooner even though I now have a warmer and drier workshop now, with a beer fridge.
For the final coat I always hope for a dust free day, have even wetted the floor down, apply it and walk away.
Should have said I use a degreaser and tac rags when doing the final coats as there will always be dust.
If you are going to cut back the final coat with 1000/2000 grit wet and dry and even polish it leave the varnish to harden. I leave at least a week or two for any final fiddling if it is needed.
I always paint and varnish under quite harsh fluorescent tubes, they show every imperfection, so if I get it to look ok under the harsh lighting it means it’ll look fine in daylight.
http://www.cvrda.org/idiots-guide-to-varnishing/