Designing a home automation system

Hi guys. I have a cottage that I’m renting out to tourists. As I don’t live in the vicinity, I have to rely on other people, and would like to automate as many things as possible, especially related to heating. The heating system is decentralized, comprising AC units and electric heaters (and an electric water heater I plan to replace with a heat pump boiler). Electricity is expensive, of course, but I don’t really have a feasible alternative for a number of reasons. I plan to install a large solar panel array, but even so controlling electricity usage is very important to me.

I need temperature sensors, window/door open/close sensors (to switch heating off when doors/windows are open for a few minutes), on/off switches (preferably to install on the power cord itself, so they cannot be uncoupled - I’m using Sonoff’s WiFi devices with built-in temperature sensors at the moment, and they work fine, but I think I need to add external temperature sensors to be able to achieve the level of control I need - like setting different temperatures for day/night and so on) and smoke sensors. I would like to keep the price as low as possible (needless to say) and use open-source solutions - because I don’t like to rely on proprietary software, and because it usually doesn’t offer the capabilities I need. What would be my best option? What devices work well with open source software? I made a simple diagram for myself to visualize where things would go:

Finally, I wonder if it’s possible to avoid using my AC’s app (Gree) - it’s just terrible… though I can live with that, as it’s not all that important to fine-tune temperature settings since these units are quite efficient. Would the unit get damaged if it were repeatedly turned off and on by a switch instead of self-regulating?

Do you use the gree integration?

If you want wifi and like open source, this could probably be all done with esphome.

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Thanks a lot! I’m really surprised there is a simple solution for the Gree mess. This helps me a lot! I’ll look into ESPhome. Can you recommend any specific hardware that would be easiest to configure and cheapest? I’m thinking of temp sensors, door/window sensors, smoke sensors and on/off switches. Do you think it’s a good idea to invest in a fully low-freq ecosystem with a bride or is wifi a better idea? Unfortunately I don’t think bluetooth sensors like the cheap xiomi ones (temp) that can be had for 4EUR and hacked are an option, though I would have to test if they can cover the distance I need. Currently I have a phone in my garage with all the apps installed that I remote into, but, obviously, I’ll buy some kind of board or maybe a low-power laptop to handle server duties and communication. I’ll probably have HA as a docker or traditional install on Linux as I’d like the server to do other things as well. Maybe a stronger bluetooth receiver could help with those bluetooth sensors, I have zero experience with the protocol, to be honest, other than hooking up a BT speaker to my phone ; )