Hey Jens,
Can you give more information about your system, like rpi model, processor, ram?
Do the logs show anything tor related? I think you can type
$ journalctl -g tor
Can you run htop while you start tor? What do you see?
One last thing that’s maybe more important. It looks like you are running tor 0.4.7.16, which is now end of life:
Worth noting, among few minor bug fixes, directory authorities running this version [0.4.8.11] (and above) will automatically start rejecting relays running on version 0.4.7.x which is now end of life.
Can you update tor and try again?