With those dimensions, it sounds like the seating will be against the backwall. If so, just skip the surrounds. Just get a front-stage setup. If the seating has to be against the backwall, invest in an acoustic absorber to place behind the listening position.
After that, if it were me, I would just get a set of Polk Reserve R700s and skip the center and sub. Or maybe grab a pair of the HECO Aurora 1000s if they can still be had, and get an affordable sub with deep extension like the Hsu VTF-2 mk5 or RSL Speedwoofer 12s with the HECO speakers. The Polks do not need the assistance of a subwoofer.