http://www2.usfirst.org/ftpdoc/coordination/
Check out the above information from the Robot Quick Build Session. There is a LOT of great info on this FTP server.
Before turning on the power, you'll definitely want to have your mentor check out your wiring job.
Regarding wire size, I use the following link very often to compare gauge (related to wire diameter) versus resistance and current handling capacity. Larger diameter = less resistance and more current capacity.
http://www.powerstream.com/Wire_Size.htm
Russ