Home App and Multiple Wifi SSIDs

My home network has a primary router (in router mode) and 4 secondary routers (in AP mode). All of them are configured to use both the 2.4 and 5.0 ghz wifi settings, but rather than having them use the same SSID I have them configured so an end user can select the SSID they want. For example, the two SSIDs are something like wifi-24 and wifi-50. All the routers (regardless of mode) are set to use the same password so a user can roam between the various locations and things work just fine.

I the main house I have several HomeKit devices that attach to the 2.4 ghz wifi network and devices that attach to the 5.0 ghz network. I have, for example, three HomePod Minis, an AppleTV 4k, and numerous light controllers and switch controllers. Some only support 2.4 ghz, others support 5.0.

Usually, the Home App sees and controls all of the devices just fine. But, sometimes some of the 2.4 ghz devices show "not responding" and I have to manually reboot them.

With that preample, several questions.

1) My understanding is that as long as all the devices are on the same subnet they should be able to work seamlessly with the Home App. Is that correct?

2) As long as routers are not configured to isolate devices between wifi networks (2.4/5.0) the Home App shouldn't have an issue with devices being connected via different wifi frequencies, right?

3) Can I force the "main Home hub" to be on a device (like the AppleTV 4k)? Or does the main hub roam depending what device if turned on? For example, the HomePod Minis are on all the time, but the AppleTV 4k gets shut down when I am not watching anything. When this happens does the "main Home hub" shift from the AppleTV 4k to a Mini?

4) Assuming my routers don't reboot for some reason (like firmware updates) and that my HomeKit devices don't reboot for some reason, why would the Home App have connectivity and then lose it randomly?