It seems to use port 22222, at least that is what the verbose output says.
I decided now to shut down the system, mount the hard drive under windows and edit the config.txt there. Apparently that is easier than to get ssh working…
As a side note, I just realized that the raspberry pi case fan, the raspbee 2 and the HM-MOD-RPI-PCB all want to use the 5V pins of the raspberry pi. So I ordered the ConBee 2 and the HmIP-RFUSB and then there is also no need to configure the gpio pins anymore 