I can well appreciate why your head hurts.
There is literally almost no limit to what you can do, with that space.
And yet there might very well be limitations, if you think about best practises and things like properly being able to light up a massive screen, and how bigger,
means the need for a brighter/pricier projector. Budget, and where you might potentially apply your dollars might sway the final design.
One other thought is will you actually fill what could easily be 15 seats on a regular basis? That space could be two rows of five seats and every seat could be 5' off of a speaker.
And you could still add something like four "flex" seats, as occasional overflow seats. Your speaker's capability to play reference levels over what could be 20', might be expensive
and limiting choice. (Or simply mean very diminished third row performance.) The flip side to this, is maybe one less row is better overall performance, and the savings of five seats,
I doubt designers start with golden ratios. They start with the seat itself, and a seat count. And I am sure they work hard to hit a right balance of performance, while working to avoid
near multiples of room dimensions. They also make sure seated ears avoid areas that suffer from a lack of smooth audio.
Poster and glass in the room also are acoustically reflective. Not such a desirable feature, in my opinion.
A 72 degree front row is ergonomically a mess. You want your eyes to be able to take in the entire screen, at once. You do not want your eyes jumping around a screen to follow the action.