I think that Carey makes a serviceable LT but hardly a good one because he played guard in college. You seldom see college guards move out to left tackle because it requires so much speed and quick footwork. You frequently see the opposite: a good left tackle in college moves inside to guard in the pros. The best college non-tackle position to yield possible left tackles: TE. I think moving Carey to LT is a stop gap measure pending the development of either Alabi or another youngster from day 2.
Any Day 2 tackles -- or any lineman -- taken are going to be projects who take a year, maybe two or three to be ready to play as starters. The Fins might also take a big TE in the 7th or even sign one as a FA to find a good LT (the Bills signed Jason Peters as a UFA as a TE -- he wasn't much of a TE, but he sparkles as a LT!).
I think that maybe the Fins' plans were disrupted when not only Joe Thomas but also Levi Brown were gone by #9. Then Staley got snapped up before the Fins chose in the second (might have been late first). In a way, I'm not surprised because with the dearth of good linemen, especially at LT, coming out of college, the relatively few good ones get picked up fast.