Just a couple basic suggestions. Go ahead with at least 12 ga wire for the speakers all around. You might even consider heavier for the front speakers. Also, I would use RG6 (coax antenna cable) for the sub instead of regular "composite" (not really the correct term, but people will generally know what you mean) cable. You can put RCA connectors on the ends to use it.
This should really be in the HT Construction section. Maybe a Mod can move it for you.