I plan on Two rows of seating most likely four across. And if the fronts are 11 ft apart then I will sit close to 11 ft away if 13 ft apart then I will sit 13ft.
Unless you are willing to move seats around between single and multi-viewer seating you will not have any one seat in the sweet spot, equilateral triangle with the mains. Also if you plan on mostly HT and not as much 2ch music then the equilateral triangle becomes less important though not totally irrelevant as you add more speakers. If you want to optimize for multiple viewers then you would want the apex of that triangle falling in the middle of your 4 center seats or even a little farther back IMO. The reason I say that is that in my experience I’d rather have the mains a little wider rather than a little narrower if I had to pick between the two.
My biggest concern is, 92" or 102" Front projection or 60" Plasma.
IMO and that of THX, a 60” plasma will look tiny at 11-13 feet. http://myhometheater.homestead.com/viewingdistancecalculator.html
The THX ideal seating distance for a 102” diagonal 16:9 screen would be 11.4 feet. Obviously this isn’t a hard and fast rule but a good place to start from. However, the larger the screen the more light you’re going to get reflected around the room. OTOH the smaller the screen the less “movie-theater-like” the presentation and the less it will draw you in because it will fill less of your field of vision. I hate reflected light but IMO the immersion of the larger screen more than makes up for it.
Also since you plan to have your main speaker 11-13 feet apart a larger screen will keep the picture and soundstage in sync. With a 60” plasma and speakers 11-13 feet apart some of the on screen action will sound like it’s coming from several feet off to the side, something I find very distracting. I find that keeping the mains within a foot or so of the edge of the screen works best.
Can I place the M80's butt up to the subs or should I allow a ft between sub and M80.Actually I have my M80 planned at 4.5ft from the side walls if I place it along the 21 ft wall. if against the 15.5 then things are going to be tighter.
As long as the subs aren’t blocking the M80s drivers I wouldn’t worry about that. Hell you could even put the M80s on top of the subs to see if you like how they sound elevated. It might go well if you plan on having the second row of seats on a riser. However, the advantage of using two subs is to even out the bass response of the room which is often best achieved by placing the subs opposite each other. So if one is in the front left corner the other might work best in the right rear corner. Opposite centers of each side wall and even the front and back wall are also generally superior to left and right front corner placement for bass flattening. If you don’t plan to use the dual subs for bass flattening then I would save my money and only get one. IMO using two, unless in a very large room, is a waste if you just want it louder, and then if it’s louder you want a single EP800 would probably do better than dual EP500s.