I will definitely want a good digital scan as a back up. My plan will be to colour it with watercolour. There are a couple of steps in the preparation for painting it that should protect the pencils from smudging but still allow the watercolours to permeate the shiny graphite. I bought some very expensive Ox Gall liquid and a few drops of that added to the water I use to soak the paper before stretching it is meant to reduce the likelihood of the watercolour beading on top of the graphite.