First of all ... Welcome to the forum :wave:
Front speakers (L+C+R) need to be at ear level (36"-42") if possible, and surrounds 2'-3' above ear level (5'-7' from floor).1. What is best height to mount the speakers?
No, if you have just one row place them in the same direction of the seats, if you have two rows try a little behind the first row or between both rows; back surrounds in the back wall (look at this Speaker placement guide )2. Should I center the side speakers (middle of the 16' walls)
At least 14, for longer runs (50'+ use 12). www.monoprice.com is one of the cheapest places, you can also try Lowes or Home Depot (100' 16gauge $25)3. Recommended speaker wire
This is a little more complicated ...What is your budget???:bigsmile:4. Recommended speaker system that is reasonable but provides great sound.