Home server?
I have a dedicated home server that runs Unraid. It is primarily used to download and host media (Plex, sonarr, radarr, etc.) but I've also found it can be used for home automation purposes.
You can run Home Assistant in a VM/Docker. I primarily use Hubitat, but have a "Echo Speaks" plugin self hosted on a docker container.
Be prepared to be waiting a while.
You don't need a pull chain fan.
If you have separate wiring for lights and fan, you can use a remote controlled fan as long as it is AC-powered and has a separate remote receiver in the canopy. You just bypass the remote receiver and wire the fan directly to AC power, then the Lutron fan switch acts as the speed controller.
This applies to any AC fan and wall mounted fan switch. I've done it several times. It works perfect (and looks better than pull chain fans)
any risk of "feeding the fire" is operating under the assumption that all the oxygen has burned out of the space, so the occupants are already dead at that point.
Not completely true, wind will (airflow from a whole house fan) spread fire. There is a reason fire danger is increased as wind speed goes up. It allows heat to spread horizontally instead of vertically which leads to combustion of surrounding materials. It leads to bigger fires more quickly.
You should do the opposite. A large amount airflow will give more oxygen and airflow to fire and will possibly allow embers to spread. In commercial buildings, the fire alarm is often tied to shutting off the HVAC upon an activations.
Besides that, one of the first things firefighters will do upon arriving on scene of a structure fire is turn off the electricity and gas to the home. So, all you fancy automation will mean nothing and they will still probably cut a hole in your roof.
Hubitat.
Agreed. I would categorize myself as a similar profile to the OP: a nerd that has set up very complicated systems, formerly worked in IT as a desktop support and network administrator, and runs systems with multiple OSes in my home, but NOT a programmer and Home Assistant is one of the most difficult pieces of software I ever tried to use. The user interface is anything but easy. There is no useful documentation despite everyone claiming there is. The UI is pretty but the UX is garbage.
I'm running Hubitat and it works great. I have setup complicated automations with no issues whatsoever. Every few months I try to dabble with Home Assistant with the goal of moving over because everyone here preaches about it's greatness, but every time I get frustrated, give up, and stick with Hubitat.
Which TV and which speakers/receiver?
With most modern TVs/Speaker setups this is possible without any additional hardware using HDMI-CEC (each TV manufacturer calls it something different for "branding" but it is all standards-based)
I haven't kept up on it, but didn't Logitech discontinue the harmony hub? Is it still supported in any way? for how long?
What is the ultimate end goal?
You probably aren't going to find a "doorbell" that will seamlessly connect to a relay... as a "doorbell" isn't designed to do that.
What you can do is find a wireless button and a smart relay and a way to link them together, that will probably need an intermediary (zigbee hub.)
I think you missed the point. You are overcomplicating something with a much easier solution.
You already have a "smart" switch. Make your programming smarter to avoid the problem instead of a using a complicated workaround.