Why would Peter of Married Gwen? He probably would've never came out of his shell if he didn't become Spider-Man, hence he would've never met her.
Also I like the idea, but not the idea of giving their powers a characteristic. They're powers helped in a big part of changing who they were in life before they got them. In this type of scenario I'd picture older characters like Reed Richards, Victor Von Doom, Steve Rogers... basically any original Avengers as teachers of the School. Reed and Doom as Competing Science Teachers(they didn't get their characteristics from their powers so they'd basically be the same) and Steve Rogers as a gym teacher. various X-Men, Peter Parker, New Warriors, Young Avengers, New Warriors as Students. Moon Knight and The Punisher as the schools creepy off beat Janitor's or something.