I had to buy a special HDMI switch because my projector is eARC-naive, but my understanding is that a lot of modern TVs are eARC-aware and a special switch is not required. The one downside to my setup is that I have to press a button on the HDMI switch to toggle between the PC and the AppleTV, no remote control, but hey it's good to stretch your legs now and then right?
Re audio quality, I really like my big HomePods and find they fill the room quite well and have a solid low range to them. I'd also agree that the HomePod Minis are not suitable for a living room entertainment experience.
No issue whatsoever, latency is fine, but a little too high for shooters and the like—but I use headphones then anyway.
How is life in the Sonos ecosystem? I vaguely recall there being some controversy around them a few years back, and I'm generally distrustful of third party hardware companies attempting to write software.