Also I thought that Green said that they wont take a RB (Arrington in 2nd) if they do the deal with Buffalo
You're right.
Re Castillo - The fact that he was up front about it apparently impressed a majority of GM's surveyed. Whether or not the Cardinals were one of them is debatable. All I know is: we need a NT badly, he seems to be good value at that pick and there aren't many good NT's available in this year's draft.
Regarding a guard at 2 - You may have a point about Green's MO, but I also know he says he'd take the BPA at each rung of the draft and, in my opinion, Baas comes closest to fitting that profile at #44. Also - he projects as starting immediately, and I'm not 100% sold on Bridges at RG.
Finally, I am not aware of any hard and fast rule that says "you have to pick up impact players in the second round." (I do know that many teams believe this is what you do in round one).