I read a paint manufacturers guide book once and they specifically stated NOT to wash the fuse with any form of soap or detergent-( I seem to recall thats an old airfix model suggestion) the reason being you add another layer of grease to the surface, which is almost impossible to remove.
They suggested using a rag with the strongest thinners you could find and wipe down with a three fresh rags. The first stage merely dissolves any mold release or grease and moves it around, the second wipe removes most of it and the final stage should leave you with a clean rag, with all the grease having come off in the second stage.

I used Urethane thinners on my modellbau mirage, which seems to clean easier than white spirit.

I cant comment on what grit of paper to use.