How many teams, 12?
Unlike some others on here, I'd still be looking to tweak your SP staff. It's great on potential, but has substantial downside if Bonderman doesn't improve and Penny and/or Burnett prove to not be 100%.
I understand (and agree with, to some extent) the whole MR strategy, and you have some very good ones, but I think they are taking up a bit too much space. Urbina and Percival will probably only help you if they are closers; if (or when) it becomes clear that one of them won't be closing, you need to punt 'em via either trade of ww. I'd use that spot to get a 6th SP for insurance.
A for 3B, i'd be pretty worried about going into the season with McP as my starter. Young guys w/ hi K rates can really get into funks (see Pat Burell), and he is already suffering from injuries. If you think Blake will still be on the WW when they place McP on the DL (as GoToWar suggested), then wait; otherwise, I'd grab Blake now.
Also, I would not deal Pedro. You've got two stud SPs already locked up, why mess with that?