Go with Qgis, there a loads of well written tutorials for using it and even step by step guids to do what you want: Example.

You can take ot a step further and host your maps online with either qgis2web like This, by using the build in tools or geoserver. You might even take it to the real world with qfield or an ar tool.

That’s where occupancy sensors shine. I generally don’t have to touch my phone or switches.

If you need something running fast and easy buy a synology nas. Not the best hardware and expensive geat if youi dont have the time to mess around with stuf like unraid etc. There a lots of great guides on setting op docker containers on that. https://drfrankenstein.co.uk/ is a geat example of easy to follow guides.

Amagettron advanced en soldat are fun games (not sure if they’re open source)

Look into open therm gateway with something like a dumb Honeywell Round modulating thermostat unless your thermostat already supports open therm.