Personally I have zero interest in Harry Potter stuff, so I’ll leave that scene for others to plan.
But my son just mentioned an interesting idea that I feel is worth considering. Have you seen the chocolate factory ride at Hersheypark? You ride a little car past various chocolate-making machines: giant mixers, conveyor belts, labeling machines, right through a drying oven…it’s really cool. (Goofy in places, with singing cows and such, but still cool.) Something like that could make a pretty neat modular display. (The ride itself is modular, divided into rooms.)
If you haven’t seen the ride, here’s a video: http://www.youtube.com/watch?v=BLUEptVYHN4
It’s not a very good video. You might want to just turn off the sound and watch from 5:45 to 7:30 for a taste (har har) of the experience.