HA isn’t the only option. I think there’s two other open source smarthome solutions out there(?) And you could probably do with just an MQTT broker and a Python script, or something like that…

But HA isn’t a bad choice. They’re doing a phenomenal job. And related projects like ESPHome make it really easy to integrate microcontrollers. And if you want to do more smarthome stuff, it has a plethora of features, integrations…

Extra hardware isn’t absolutely necessary. I have one server at home which does NAS, and I use 4GB if it’s RAM to run a virtual machine with Home Assistant. That’s enough for the entire thing including a bunch of Addons.