Your description is very similar to how my room is setup currently. My rear seating row is up against the back wall with the rear surrounds mounted as you mention. They are apart about the width of the couch. The side surrounds are mounted a little higher and angled down toward the listening room using the Axiom mounts. Don't worry about not having one wall open, at one point before I enclosed my theater will walls, I had 2 sides wide open.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85