Okay, so, I definitely had to look this up, but OH EM GEE. How sweet! I mean, okay, fireworks are maybe a little overkill. And who really wants to spend time afterward cleaning up all that confetti?
I would say, since this is your first prom and promposal, keep it simple! Flowers are totally sweet. Chocolates are also a plus. I know those are usually for Valentine's Day or whatever, but who doesn't love chocolate?
You and Em - duh, I definitely saw who you're asking and super cute! - don't seem like the over the top kind, which is totally fine. Definitely simple. Definitely sweet. I think you'll knock it out of the park no matter what you do, though.