Mark, welcome. On your side walls/back wall question on the positioning of the back surrounds, first let the point be made that in a 7.1 setup the side surrounds should be directly to the side(not farther back)of the listening position, maybe 3' above ear level. Then, the back surrounds should be separated about as much as your distance from them. Usually this would call for mounting them on the back wall, but if the separation requirement can be met with a mounting far back on the side walls(almost at the back wall)this works well too.
