Bayern signing Hummels is a huge get. I wouldn't even think twice about the fee as this is how it is these days even when a player has only a year left on his contract. On top of that Hummels is still relatively young and if he's good for the duration of his Bayern contract he'll have been worth every euro.
Hummels and Boateng, assuming they maintain their level, will be a top notch pairing. I've said it before, but it's just another example of top CBs being consolidated at the top clubs. And now in Bayern's case they not only arguably have the best CB pairing out there at the moment, but also the youngest proven top CB pairing in the game right now.
Ancelotti looks to be inheriting a better Bayern than Pep did. If he indeed has told Goetze he's not in his plans (which at this stage is odd news and were it Pep it'd be some sort of moral disaster) then that's on him though. Anyway, it'll be interesting to see what Bayern still do this Summer. They have a few players they can offload who even if they don't bring a transfer fee windfall will free up a ton of money in wages.
As for Hummels choosing Bayern, people criticizing him need to consider a few things. He and/or his girlfriend/wife probably prefer to remain in Germany. On top of that he was in the club's youth ranks for some time (I'm not sure how long though). He's also going to a club that challenge at the highest level (not that BVB is too far off, but I don't see them challenging as Bayern do). And this is coming from someone who finds the move mildly disappointing.
He'll never see the field. He'll never become a starter for Barcelona. Stupid decision by him. Also, where does that mean for Ben Arfa?
Of course he'll see the field. With injuries and rotations he'll definitely get minutes as this season demonstrated. I'm sure someone will be leaving as well which will help him get minutes. Ideally about three players would be sold instead of just one though.
As for him ever becoming a starter, that remains to be seen. I think it's fair to question him being an undisputed starter in the future, but I wouldn't rule it out entirely.