What should I wear to the Harry Potter film release?

Ok, my friends and I are all dressing up for the Harry Potter film The Half Blood Prince and going to the midnight showing. We all have chosen to dress up from different houses. I picked Slytherin! We are all wearing the Hogwarts uniforms or kind of. It just depends on if we can find the clothes. Well I am going to dress up ier than the others because I am Slytherin and its the bad house. I am going to wear a short black pleated skirt, white on-up shirt, and the Slytherin tie. I can't decide if I should wear black stockings with a garter or thigh highs or just knee high stockings with black heels. Also I don't know if I should wear closed heels or open heels. So please help and tell me what you think also! Thanks!