realistic to me is that things happen that really would happen to your character
Carter didn't have a very elaborate one when I first started, but I've added on and he has a pretty solid background.
As for the relationship thing. I agree, things shouldn't be serious for the younger students. But I did have a little boyfriend when I was in middle school. We'd walk to class together and hold hands and go see movies and it was super cute. So that is realistic to me. I started liking guys in 5th grade, so for Carter to have a little first year girlfriend is realistic to me. What isn't though is huge age gaps or people in 4th year or above going out with like first or second years. When I was that age guys that much older than me wouldn't look twice in my direction.
And I agree that if you're using a popular cannon last name to kind of work out a family tree.

And those are my two cents.