A) Lynch wanted out of Buffalo and Fred Jackson is not a long term fix at RB so RB may not have been an immediate need but it wasn't all that terrible. Considering there wasn't a QB, OLB or OT worth that spot, it wasn't all that bad of a pick.
B) He hasn't contributed because of Lynch. He's now gone so you'll be seeing much more of him.
C) Should've traded down. Yea, cuz it's SOOOO easy to trade down. I hope you understand that in order to trade down, we have to find another team that would want to trade up and pay the money for a top 10 pick. Not many teams are willing to do so unless they see a prospect that is a can't miss.