: Which finish can be worked to the smoothest finish? Epoxy? Varnish?
: Paint? I want to squeeze all the efficiency I can out of this
: hull!

Actually for best efficiency, whatever final coat you use, sand it with 400 grit and leave it sanded. The tiny scratches carry a thin layer of water with them as you move through the water and creates a friction buffer between the hull and the water. Sailboat racers and suffers have done it for years. The idea is similar to the dimples in a golfball, but google it and I'm sure you will get plenty of info.

As an example, take a smooth, glossy hull and wet it. Now rub your hand over it. Then sand it with 400 grit and wet it and rub your hand over it. The sanded one will let your hand glide over it. The smooth one will have friction.