Great activity!
I also like to include the height of the ISS (about same as Hubble), GPS satellites--12,700 km, and 'satellite TV' satellites (geostationary)--35,800km. Only downside of including these is that the GPS satellites would be 16 m away, and the geosynchronous satallites would be 28 meters away--so you'd have to take the model out to the soccer/football field!
