A good finish starts with a good brush. Expect to spend at least $20 and maybe as much as $30 for a good brush. I prefer synthetic bristles. They don't absorb as much finish as natural bristle which cause brushes, like hog hair, to become soft and limp. Try to find a good Chinex brush. You want a brush that will allow the finish to flow smoothly. When looking at brushes, pinch the bristles just above the ferrule, or below depending on how you look at it. Cheaper brushes use wood or plastic spacers to make the brush look like it is fuller and has more bristles that it really does. There will be some space, this is called the reservoir, but too much is a sign of a cheap brush. Also, take the brush out of its package and swipe your hands across it o make sure no bristle fall out.
You don't need to do anything to the wood, but it might help to raise the grain first. Just wet the wood with water and sand once it is dry. This will help cut down and the amount of sanding you have to do once you start finishing and leads to a nicer finish.
320 grit is a good choice.
When applying the finish, you want long, smooth strokes. Hence, why you want a good brush. Keep the foam brushes for......on second thought, see if you can sell them.