I’ve just finished a complete writeup of my automation setup. I am slowly gutting and rebuilding each room of my house and in the process, building in automation. Meaning all wired (WiFi is temporary at best), almost 100% MQTT (stable, no worrying whether this or that integration will stop working), almost all my own hardware designs and 100% open source. Of course with Home Assistant at the core.
It covers how I host Home Assistant Core, my own I/O boards to control relays and take inputs, building automation into rooms (conduit, conduit, conduit) and designing a system that will be reliable for the longest term possible. It’s almost a website within a website so set aside some time, grab a drink, and I hope you enjoy!