Bought 2nd hand AppleTV, Privacy

What I would do is:

• Have only 1 library
• Make sure that iTunes is configured to keep all your media organized (and point your single iTunes Library to your preferred disk)
• When adding files to your iTunes library hold down Option/Alt to let iTunes know that it shouldn't copy the file to where your library is

This way all your data will be organized by iTunes except for the large files that should belong on your largest external disk in the first place.

Cheers...

I would suggest, assuming the main function you'll be using is AirPlay, that you give each classroom's Apple TV its own AirPlay password that only the instructor in that room knows. That way, he/she can connect to it with the credentials you've given and no one else can. If a student needs to connect to it to show something, the instructor could put in the password on the student's laptop. Obviously, if the password gets leaked you can change it at will.

I know this seems a little tedious, but I think it's the only way of doing it short of re-subnetting the building (I understand why you'd want to NOT do that!).

Also, I would suggest you create DHCP reservations for each Apple TV on your DHCP server so they always get the same IP address when connecting, just in case your network gets overloaded. Just a suggestion.

Hope this helps a little. Good luck.