I like the 80 grit to start, remember do not sand into the fiberglass, sand along and away from the glue line. A good work bench and padded clamp makes the sanding strokes more equal and efficient. I count the strokes. This will mess up your nice handle work, are you sure you want to do that? I suppose you can wrap and tape off that portion. I use super fine sand paper on guitars, I have to do a patch on my concert guitar neck, the guitar body is french polish but the neck is a fancy lacquer, I can fine sand that stuff to 1000 grit and it will stick. For bow limbs 500 grit is fine enough. I do better with moderate pressure with cutting sandpaper than doing more and harder strokes with lighter sand paper. If you are just going after the corners and are worried about going too deep you can start with the less aggressive grit, like 100 and then go 200 and finish with 320 or so. Careful to leave a good lip for your bow string loops.