Big room at 8000 cuft, you'll need some significant subwoofage.
Where is seating in relation to the television wall? Floor is concrete? Surfaces reflect, they matter, as well as your furnishings...
As far as video content personally I'm sticking with 1080p/bluray for my needs for now, little content in HDR/4k, will wait until it is more widespread or perhaps just skip it for the 8k/16k or whatever's next
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. You staying with a tv or going with a projector?
Are you wanting to do the ceiling surround speaker thing for the latest immersive audio experiences (Atmos, Auro, DTS:X etc)? Speakers behind you in a room that large would likely be a good thing, you usually want 4-5 ft between your seat and rear surrounds. Need to know your seating plans, tho.
Sonos is more about wireless needs, not HT so much. Klipsch can be okay, personally does little for me but supposedly the RP series is nice, I like some of their old large legacy stuff. BestBuy isn't as good as the internet IMO, altho BestBuy or Fry's (and other big boxes) can be good on sale, not for knowledge so much.