I had to use the 3M pad on the first one I did, then I started putting a couple gallons of water in the keg before plasma cutting the top out. This cools the slag instantly and you just dump it out. There might be a little spatter on the sides, but much less than if dry.
I'm just starting and also using gifted/saved bottles. I went straight for a bench capper rather than the handheld. It works great but it definetly helps to sort bottles by size as you cap.