Using HomePod w Apple TV

Yes one will work. If you get an Apple tv 4K you can set the HomePod as default audio. There are 3 models of the 4k, the second and third generation can be plugged in via ARC HDMI port (if your tv has this port) and this will also allow you to use it for all tv audio output. I’d advise getting the most recent model if you can, so it supports the latest features that get released in subsequent tvOS updates. I’m sure you’ll enjoy the sound and can decide later if you want another HomePod to stereo pair. (You must have the same model of HomePods to stereo pair).

Sone info: Use Apple TV to play audio throughout your home - Apple Support

Set up home theater audio with HomePod or HomePod mini and Apple TV 4K - Apple Support

Use HDMI ARC or eARC with your Apple TV 4K - Apple Support

Set up a HomePod stereo pair - Apple Support

you can pair two in stereo and use them, but you can't do some fancy 7.1 surround setup with enough homepods