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).
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 )
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)
This is a little more complicated ...What is your budget???:bigsmile: