IMHO RB is a big question mark for the team. Cohen is good, but not a high volume guy. Davis has never been a high work load guy. I like Montgomery, but how much do you want to rely on a rookie RB?
Your comments on RB are surprising to me. RB is probably the position I would most rely on a rookie. There were probably 10 rookie RBs last year that had significant roles with 4 at 200+ touches.
Even if Montgomery goes down, I would be comfortable with-
Davis
Cohen
Patterson at RB
Whyte/street FA
-as a stop gap.
None of them are volume guys, but I don't know that this offense really benefits from a volume guy.