Had to look up 3 gun on you tube. Looks fun. Uspsa website isn't much help. Gonna look into steel first and see how he handles it and likes it.
You'll get a lot more of the appropriate eyes for your questions if you take them to the Shooting Sports Forum.
Lots of details on USPSA info on http://forums.brianenos.com/ . I'd look locally on INGO first though.