I great fan of Tolkien could only wish for a look to the beginning of the entire history. There is a wealth of drama and great story line in the 1st Age of Middle Earth. Why make up new story lines when there is a wealth of history to draw from, most devoted fans are dying to see the battle of the first Age of Middle Earth. Unless of course the plan for the entire history of Middle Earth is comming after the Hobbit and it's sequel movie.
I like your overall ideas, but wondering about Gollum. And also the One Ring. In fact, the ring is a "character" that could be more fully developed. And while the ring was created with much of Sauron's essence, the ring in turn made Gollum into the creature he is today. Your plot points would certainly provide the grand scale cinematic experience, but I think Gollum's journeys (of sorts) would make not only an interesting sub plot, but provide a content bridge that remains consistent both in details and themes to Tolkien's works of both The Hobbit and LOTR.
i like the ideas here, to the person who wrote about ideas from th silmirilion, sadly no ideas can be used from that book as the film makers do not have the rights to that book so stories must be created from things that are mentioned in lotr and the hobbit.