I don't know. They have the restaurant car on some trains so that's another 2-3 people, and I really have no idea about their operation so I added some buffer. I wouldn't expect there to be more than 8 on a train unless it's some special event.

For some high speed routes there’s a limit on how many carriages one attendant can supervise (maybe to ensure timely evacuation?) so a 12 carriage ICE train needs 3 attendants to fully operate.