Size of fuse isn't really an issue, I usually use the same size of the fuse as all of the ones inside the amp together. Its mainly there as a safety precaution incase the power grounds out. My amp has 4 20AMP fuses so I would use an 80-100 amp fuse, since the amplifier should never draw that much anyways.
Also for future reference on soldering you take the board out and remove the solder from the back of the board and the caps come off you don't cut them with a dremel. Plus that makes the holes open for you to put the new leads into and solder them on the back as well.