After all, I build my new system on a Raspi 4B 8GB and modified two Din-Housings so it fits to the fusebox. (In the first, I want the two components in a row, but the wires are to short ther's not enough space for the cases...)
I used https://sensorsiot.github.io/IOTstack/ | https://github.com/SensorsIot/IOTstack as a basis for the docker containers and I had to install homeassistant with the help of the script manually to figure out some issues...
To control the raspi without keyboard/monitor I added parts of the RackPi --> https://www.thingiverse.com/thing:3022136
(My girlfriend modified the front sheet, so I had the chance to place the Raspi to the bottom of the case with the cooling fan on the top...)
(The Switch changes the voltage of the fan between 3.3V and 5V. 3.3V works fine and the Raspi actually has about 36°C...)
(The lower case os the housing for an original Raspi power supply. I opened it and fixed it on a circuit board. With a little switch I can turn on a LED to check if there is power on the device. The power supply is on fuse 24.)
(I also added an adapter from 3,5mm Jack to RJ45, so I can use the audio output in another room. (Our flat has network sockets in any room. They end up under the fusebox...))