1. Will you continue to use the old body? Will you be on the phone trying to help your daughter do stuff with that body? Some of the cameras have the buttons do almost the same thing. Some do not. I belive most everything is the same between the D5200 and D7000, but I dont' know about the 5100. The D80 and D90 I have access to are different enough to be annoying.
Run your questions past http://www.nikoncafe.com/vforums/index.php
Lots of good people there.
One day, I shall come back. Yes, I shall come back. Until then, there must be no regrets, no tears, no anxieties. Just go forward in all your beliefs and prove to me that I am not mistaken in mine.