1. Don't try to wipe these off yourself without some tutoring, or you could damage the very expensive screen.
2. After you finish a roll, you wind the crank on the film back to roll up the film.
Pure intuition probably isn't enough. You should be able to find manuals for the camera and back here: http://www.butkus.org/chinon/hasselblad.htm
I can recommend David Odess if your camera needs servicing. KEH surely would fix it, or replace it, if defective.