James,
After you sprayed the undercoat, let it dry for 24/36 hours. If you didn't touch it, you probably can just use a tack cloth to make sure there's no dust. But, if you really want to wash it of, I would just lightly wipe it down with a damp, lint-free paper towel. You can find those paper towels in the super market. They actually say lint free. I think the name is Sparkle. As long as the paint had enough time to dry and you don't rub the hck out of it, things should be fine.
As far as the Future coat....Pieter's method is pretty much it. 48 hours seems to be the absolute safe time.
John