Should I dress dress up for the midnight premirere of Harry Potter?

Here in a couple weeks me and my friend are going to the midnight premiere of the last Harry Potter. We were wanting to wear our Hot Topic Gryffindor and Slytherin shirts with ties, Harry Potterish looking skirts, wands, Harry Potter glasses scar, and knee high socks to look like Hogwarts Students. I have never been to Midnight Premiere so I wanted to know if alot of other people usually dress up? I don't want to look dumb and be the only people dressed up. Should we go all out or just a shirt, because we really want to dress up. And how early should we arrive to get in line? (btw I'm asking on my brother's email if you were wondering about the skirt thing lol) Thanks for your advice! :D