Re: Birchwood prep
Assuming it's already sanded to a smooth flat finish, I would use something like PVA glue (the cheapest option at anyrate) to seal both sides, and then apply a primer like acrylic gesso or oil primer. You can sand between layers, or some people add marble dust, it depends how much texture you like. I use a bristle brush and leave the brush marks in to create tooth and texture, but it's all down to personal preference. Some people like a smooth mirror finish.
If I'm using acrylic gesso, I put down a diluted (with water) version first, let it dry and apply two more layers, putting down the thickest layer last. With an oil primer, I can usually get away with one coat, but if I do use two, I dilute the first coat with mineral spirits. The oil primer is more tricky because the brush marks flatten out when drying, so I have to wait about 15-20 minutes when it's still tacky, and put the texture back in with the bristle brush.
The acrylic gesso I use is semi-absorbent. It's a nice compromise and surface to work on. The oil primer doesn't absorb the oil paint, so it is very slick. The colours stay fresh, but it takes a little more getting use to. During the first layer, it is very easy to take a paper towel and wipe away the surface, which can be an added benefit.