How should I configure AppleTV in a shared space/living room?
Require password to buy - this keeps you in control of spending money
Don't sing in to iCloud for Photos - you can AirPlay photos from another device when you wish to show your photos.
There is no interface for reading keychain contents from the Apple TV - so unless you are worried about sophisticated hackers reverse engineering and decrypting keychains - your threat model would be one to not worry about keychain syncing for WiFi credentials.


If you're worried about game center - then you might have to not allow the device to run when you're not present. I don't think there's any control there if you leave that signed in.