Pappa, 180 would be fine on the sand paper. It will give a good bite and urethane would fill 180 in one coat, though I suspect you will be applying more. As for wiping it down, get some mild "wax and grease remover". Wipe it on wet on a small area (half a fender or so at a time) then wipe it OFF with a clean rag while it is still wet and holding the contaminants off the surface.
