I'm throwing a MASSIVE Harry Potter party... I need your ideas!

My littlest siblings are finally reading the Harry Potter books. This summer, my family is throwing a HP party to celebrate. All their friends will be invited, and all my friends are invited, and I'm pretty sure my mom's inviting some people... so we're looking at an enormous party with guests of all ages.

I'm going to do a one-day recreation of the Hogwarts experience: The invitations will be Hogwarts letters. Guests will arrive in the morning at Diagon Alley and purchase their school supplies. They'll go to Hogwarts, be Sorted, and enjoy the Start of Term Feast (a.k.a lunch). Then we'll have a handful of classes, hold a Quidditch match, and end with the Closing Ceremonies (dinner).

I've got a schedule... And now I need your ideas on how to make it AWESOME.

Feel free to go crazy here. My parents have given me full rein over their property and I'm planning on throwing money at this thing.

Any ideas?