Try tailscale for remote acess run it as a docker container. I csnt help you with the other questions.

It’s not i’ve bought two of them years ago because they have a decent spec rugged phone. The s60 was bulletproof and lasted ages and even a drop from standing height on concrete. I upgraded to a later model (i think s90) and that was a piece of shit. The quality control is crap, don’t expect software updates but if you get a good one the hardware is great. So not a scam but i would stay away.

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

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