I just started to build something here! My setup so far: Raspberry Pi 4 running Home Assistant OS.
On the GPIO-Pins I have a Module sitting that goes with the name RPI-RF-MOD. Now the Home Assistant-Pi works as a CCU3 base station for all my homematic IP gadgets.
On Home assistant I use the add on Raspberrymatic to connect to different Gadgets (Power Plugs, Thermostats, Window-Sensors) which then again are introduced to home assistant with the help of HACS Homematic(IP) Local.
Now it’s working! I plan to automate my thermostats with the HACS Better Thermostat.
It was a lot of reading for a beginner like me. But with small steps and a lot of time everything is actually quite comfortable to reach. And most important: the devices can’t phone home, nothing is able to connect to the internet directly.