As you have already found out, CA glue doesn't sand worth a damn. In places where I plan on sanding, I use the old time model airplane cement like Ambroid or Testor. Now where you want to sand one area next to an area you don't, you can protect it with a layer or two of masking tape. Grits usually starting at 100 for roughing, 180 to 240 final shaping. Above that depends on what type of finishing technique you are doing.