Just stepping back to the big picture for a second:
Back when I saw Fellowship of the Ring, I watched it with someone who had never read the books. He expressed surprise that they killed of Gandalf so early when it would have made sense to do it in the second movie after everyone had become truly acquainted with him. Not wanting to spoil the fact that he comes back, I pointed out that the books start with the Hobbit, so it really was the second movie.
I'm wondering if the movies are built so you can watch the Hobbit first. On the one hand, the basic narrative story is probably capable of supporting a viewing of the Hobbit first. On the other hand, they seem to be using a framing story which might make it more difficult. I wonder if they're approaching this to make the Hobbit accessible if you watch it first or with the assumption that you'll watch "An Unexpected Journey" fourth.