I have never used duracoat but I have used baking lacquer a few times. The amount of prep work always equated to the quality of the finished product. So I would definitely prep the slide as much as possible. Although I have has success with varying levels of steel wool versus bead blasting.

Since the plastic sights are dovetailed and not pinned I am sure they can be removed and reinstalled. I took a set off a SW9VE to install metal night sights and they looked undamaged after they were removed.