Training has begun to pull a cart

I have been having so much fun with Artax since purchasing him this summer. We have become a great team and learning so much together. I am not only learning to do jumping and dressage on him but I am training him to pull a cart. I don't have a cart yet but I hope to purchase one in the spring. I have been ground driving him and he is picking it up like a champ. I have been doing my research and one of the essential components of training a horse to drive as well is riding is getting really responsive to your voice commands and use to steering. Then the next step is to hook them up to a tire or sled if it's snowy out once they are ground driving down pat and are really obeying your voice commands. That's the next step with Artax once he's really comfortable with me ground driving him. He's picking up ground driving really well so it won't be long before I will hook him up to a tire. Here's some pics of me ground driving him and some other ones just letting him loose to graze.