I'd back Barca to beat anyone, though some teams would definitely be tougher than others. I'd say Real or Juventus would be the toughest (Real have been good against us recently, though we have been off-form, and Juventus are a defensive, counter-attacking team). Dortmund could be tough as well...
I think Pedro for Sanchez and then Villa for Adriano would have done the job (perhaps also getting another goal in the process). But I see your point. And we weren't really less dangerous after Villa came off IMO, except when we did a little bus-parking in the last few mins.
Sanchez played well, but imo Pedro should have been the one who got subbed off for him, not Villa.
Hope management give him more playing time. Don't see a reason for him to leave if he gets it.
He isn't that tall for a CB, but that may not matter (just look at Puyol, short for a CB but a fucking beast in the air).
Not to mention he's fast from what I hear, which will be great for dealing with counter attacks.