We did not have to add any new service ID"s to our Airgroup.
What we're currently looking at is doing /20 networks for High Schools, /21 for Middle Schools, and /22 for Elementary schools. Having 3 SSID's in each location (Public, Private, and Apple TV).
We have a Clearpass demo next week, but $25,000 is out of our budget. I've looked into possibly doing something with an Avahi gateway if the Multicasts get too out of hand in that large size of a network.