Both your defenses are great choices this week. I'd give a slight nod to Pittsburgh - call it a hunch, but I'd rather see the Minnesota offense play a real game before starting a defense against them.
As to QB, if you're ever going to give the ball to Carter, this is the week to do so. Playing Houston in week 1 is the equivalent of a dream date. Normally, I'd leave Carter on the bench and hope Slash can get the job done, but with a Monday night game against the Patriots in store for the Steelers, he'll be in for a tough game. I'd give Carter a shot.