21-23 is pretty standard. It's a totally personal thing. Take a screwdriver to the hill with you, start at like 21", and at about lunch, see what 22" feels like. If you don't like it, move it back. It's just one of those things you have to play around with until you are comfortable.
And yes, you'll want your bindings centered on the board. So start with both bindings in the center holes, and move outward from there if needed.