Now I have a working prototype on the breadboard. 

Unfortunately I can not test the solution not where it should be used. Today we have strong wind and rain and the rabbits refuse to leave the cozy corner in their hutch. The other fury housemates (two cats) are not moving all day and therefore a test with grey fur also did not happen, yet. The other ToDo's a merely cosmetic:

• clean up esphome configuration (yaml)
• allow setting the number of rabbits through the user interface
• green / red led to signal the status (close ok, not ok, error, ..)
• design custom PCB

PCBWay kindly offered to sponsor the PCB but due to my early mistakes I lost a lot of time which I would need now. Moreover I never designed a PCB myself, I'll need much more time to learn (and make mistakes) until my design would work.  I'd love to have a professionally manufactured PCB for this project. I am definitely interested to got that route later, though.