Compounds remove material faster than a light polish so you use compounds to remove deep scratches and/or heavy oxidation.
If the scratches are deep and there's lots of oxidation then it's faster to machine sand using some #2000 grit sanding discs on a Porter Cable followed by compounding. It's also easier on you.
See this write-up of a boat we detailed....
How to wetsand, cut and buff a gel-coat boat
As for removing old graphics, you can use a hair dryer or a heat gun, just be careful with a heat gun so you don't burn yourself or damage the boat.
See this write-up of a boat we detailed....
24' Pro-Line Boat - Extreme Marine Makeover - Oxidation Removal
