I think everything in Mark 2 is a repeat of something from Matthew, but I suppose I can take the opportunity to broaden the commentary a bit. The SAB says that Jesus healed a paralytic by forgiving him of his sins and that paralysis is apparently caused by sinful behavior. I'm pretty sure I said before in the parallel passage in Matthew 9 that I believe the forgiveness and the healing were two separate issues. (I also argued there that Jesus was God, as that question came up there as well.) Something I think could be said to further the discussion is that while it's not always true that misfortune happens to people because of sinful behavior, the latter certainly can make one more susceptible to the former. Most sinful behaviors are dangerous in one way or another, and certainly can lead to disease or injury, which may have been the case in this man's life or not.
As for the rest of the chapter, there are only a couple questions about David, which I addressed in 1Samuel 21.