It's much more than necessary. / It's much more than is necessary. Both are correct
He's so busy. He never has time for me. / He's never got time for me (last one is a little awkward, but heard)
Everyone else's problems seem more important to you than mine (do). (This is fine with or without the "do" at the end)
We've just come back from the vacation. This is fine. The definite pronoun before vacation adds specificity. Normally I would just say "We've just come back from vacation."
You can't sit here all day without ordering something. This is fine.