Sounds like a good plan...looking forward to the pictures.
If those markers you are using are solvent-based (if they are pretty smelly, then they are solvent-based) then using a wash with Future floor polish shouldn't harm the paint. But definitely do a test on a piece of scrap plastic. If you've never done a wash before, you'll also want to test it to make sure you have the proper amount of tint in the wash. Too much and it will darken the part too much...too little and you won't get much effect at all. Keep me posted!