How many emails can be associated with one Apple ID FaceTime account? How many different email addresses can be associated with one Apple ID FaceTime account?
As long as those email addresses are not tied up with other Apple IDs, I don't think there is a particular limit.

My FaceTime has 4 emails associated with it - none of them are linked to other Apple IDs -  but when I tried associating a 5th email that was linked to another Apple ID, it would;t let me of course.