We made the trip from the old thread with you, Ron. The best applicator is a professional painter, next best is a spray rig, then a spray can. Since all of those are probably out, then a brush, followed by splashing it on, followed by a 2 year old splashing it on. Really, you do not have a lot of area to do so buy a good brush and clean it well when you are done. You don't need a $25 badger brush and a good one will say that it is for varnish. A cheap one will say that it is for everything. A bigger problem usually is dust and dirt so be sure that the whole area is clean and go over your board with a tack rag right before you varnish. A foam brush is great for water based but not oil based. The easiest way I have found for varnish is to put on a thick coat and come back and take half of it back off. Putting it on thick gives good coverage. Putting it on thin gives you brush strokes. But you do not want to end up with too thick a coat so gently run the brush the whole length of the board and wipe the excess off the brush back into the paint pot. You are going to use a paint pot (old coffee can), aren't you. And pitch what varnish you don't use out of the paint pot.
The semi-gloss makes a good choice. Gloss terms are relatively meaningless because it just depends on how much talcum powder or diatomacious earth the manufacturer decided to put in the product. That's right, semi-gloss is just gloss with some talcum powder--available at any drugstore. Since the talc tends to settle, stirring well is also important. If the can is old and hasn't been moved around a lot lately, you can get gloss by not stirring very well.