I haven't done a satin finish yet Robbo, but ive done plenty of waterslide decals.

I usually do a few clear coats to seal everything up then apply the waterslide decal then apply as many clear coats over the top to seal in that waterslide goodness.

I would normally wet sand to a gloss finish, but if i were doing a satin finish I would just wet sand to a satin finish.

Other guys might have a different take on it.