Depending on if you want a very nice Finnish, Use Wet and dry 800/1200 to take the surface layer off. Of course if you have a Pwerentiei with very deep paint holes its going to need some sanding and maybe filling, if you have slight surface marks/scratches, a primer filler works a treat.
You should have no need to use etch primer as long as the top coat is still there.
And always use a mask when sanding this nasty paint..