All of the above info is good, or most of it. I'm not about to disparage anyone who has experienced success with a particular product or technique.
I built and varnished about a million sq ft of boats for 12 yrs. Then opened a cabinet shop which has evolved into an Architectual Millwork business. Anyone can build a cabinet, a door, or molding, it's the quality of the finish that sets the exemplary apart from the so-so. We used to say a good finisher could make a mediocre carpenter look great.
First thing is to buy the best (usually most expensive) natural bristle brush available. Can't recommend any as we've been spraying for 20 yrs.
Any of the varnishes mentioned above are good but one not mentioned was sold under the Ben Moore brand. It didn't have a uv filter.
I would skip the shellac as a primer or undercoat and go with a vinyl sealer. This is a very quick drying product that is a great filler and will lend some water-resistance. Don't use a good brush, it will require lacquer thinner as a solvent unless you throw the brushes away. Personally I don't do well with polys, one of my finishers does wonderfully with it though. I'd use a high gloss natural varnish, much harder without the fillers needed to dull it, then a satin, 60 to 80 sheen, for the finish coat.
The vinyl requires about a half hour to sand and the varnishes about 24 hrs.