Thank you @mfalkvidd! I have been busy and had many issues to figure out for myself, but I still can't understand how binding with openHAB works. How does the information from nRF24 get to openHAB? I have MySensors Binding add-on installed in openHAB. I would be very grateful if someone could help with this last step. After this my first little sensor will be ready to go live.

Do you have a part list? And maybe you can sell one of your PCBs? ;-) I assume, the wiring is regarding to https://www.mysensors.org/build/raspberry, so that no coding work is necessary, correct? Are the activity LEDs onboard and what is the buzzer for? I'm really keen on this board ...

irq=18 worked for me for anyone who comes along wondering