If you changed any of the Hobbit, story wise it really
would be a sacrilage (I'm sure I mispelled that). The Lord of the Rings is barely suited to literature (Don't get me wrong, I love those books as much as the most rabit Star Wars fan loves that, but it's obvious Tolkien didn't write them to
sell) and so needs tweaking for a movie, but The Hobbit has the straightforward no nonsense story that only a childrens book can have.
Anyway, I'd have as many actors from the film Lord of the Rings as possible. Ian whatsisname, I forget needn't be much younger than as he is portrayed in the Shire - he was fifty when he went "There and Back Again" as it were. Smaug will be interesting to see, I always imagine him as a great golden red dragon (the illustration on the front of my first copy of The Hobbit as of an ethereal Bilbo walking into Smaug's lair, damn good it was too, so it stuck)
Rosencrantz