[eugovector]

I asked this question at an acoustics panel at last year's AES and what I got was a resounding, "It depends". It seems there is no hard and fast rule, and every designer has a slightly different perspective on it.

One theory is that you'll, first and foremost, want to work to evenly space out room modes: http://www.realtraps.com/modecalc.htm

I'd start there.

 

[eugovector]

Or just use the rule of thumb that you should sit 1.5x the 1.78 diagonal away from screen for 1080p, i.e., if you have a 221" screen, you'll want to sit about 331" or 27 feet away. I'd say your screen is far too big. Assuming your middle row will end up being 13 feet from the screen, you're looking at 104" as a more appropriate size.

 

[eugovector]

Just keep in mind that if you sit too close, you'll start notice a lack of detail, especially on anything less than 1080P. A smaller screen will have a great pixel density, and thus, will appear more detailed.

If you're going round about the screen size right now, you may want to chose that last. Get everything else in place, and start with a white wall or bedsheet to determine what size will work best.