As for the camera question, I think (though I might be wrong) the best way to do it would be to use multiple cameras in a single scene, otherwise you'd have to import your enviroment and characters into a new scene for every shot, and then do the animations one part at a time.

If you're having trouble rendering everything at once, you could render a few frames (100-150 or something like that) at a time and let your computer cool down inbetween...

But I've never done anything that big, so I'm just guessing...