Fred, everything looks good so far. I'd definitely try out the surrounds in both positions to see which sounds best. Will you put them on stands if you place them on the side?
I think you will get better bass reinforcement with the sub in the corner behind the couch. It may be more localized in that position, especially if you plan to listen to music, but it may work good for movies. You know what I'd do? Get two subs and utilize both positions!
As for the couch blocking the speaker. . .it's not ideal, but, hey, what can you do? Sometimes home decor isn't fair for those of us without a dedicated room. As long as you get some clearance over the arm of the sofa with the drivers you should be okay. Have you thought about risers to lift the speakers up a bit?
