Because you're asking this question, I would recommend working backwards starting with canvas and leather. You could go straight to 3k or 1k, but I think there's more to be learned starting up high in this situation. If all looks good under the loupe, it probably won't take a whole lot. A touch up on a Nani 12k takes less then a minute. If you need to go lower after that you really haven't wasted much time. I don't mind removing steel when needed, but I don't like to waste it.