Just be careful not to sand the plastic AROUND the repair area too much and make it "fuzzy". If you do break thru and get some fuzzy spots, you will want to wet sand those areas with some 600 grit to get it smoothed out. You would want to wet sand the current coating with 1000 grit if you plan to repaint over it, and any repair areas should be primered and wet sanded with 600 anyways.
Scuff the reapir areas with 80-180 to get the filler to stick, spread your filler, block it out smooth with 180, lay on some thick primer to seal and fill the sanding scratches, then wet sand the primered areas with the 600 and the rest of the body with 1000, and you are ready to repaint. Have fun.