Well you are lucky, NC is driving country.
You can check out one of these clubs:
Carolina Carriage Club
P.O. Box 816
Tryon, NC 28782 Carolina Carriage Club
Ned Frybarger, 828-894-0632
Central Carolina Driving Club
301 N Fallsview Ln
Wake Forest, NC 27587
Connie Hussey, 919-556-1835, email@example.com
Moore County Driving Club
Southern Pines, NC 28388
David Frump, 910-692-0943, firstname.lastname@example.org
It is good to get some help, hopefully a mentor or an instructor. A lot of clubs have clinics on teaching your horse to drive. You could advertise on craig's list for an instructor.
There is no such thing as too much ground driving, so you are off to a good start.
How about a photo of your boy?
Lets see how you are ground driving.
Get him used to contact and you need to get used to carrying a whip.