I'm a professional painter so I have every tool available to me whenever I have a guitar or bass to finish.
I much prefer the automotive finishing sandpaper as an option over Scotch Brite type pads, because you know exactly how fine the paper is. Not so with the pads.
I recommend staying very far away from steel wool. Not only will it be less consistent and less predictable than sandpaper, but the tiny pieces of metal that it sheds will get everywhere!
I'd use 1500 wet paper (and be sure to become knowledgeable about how to use it most effectively) as my first choice.
If you want it a bit duller, try 1000. A bit shinier, go with 2000.
Ultra fine sandpaper for paint finishing can be found in most auto parts stores. NAPA always seems to have the widest selection.