Your horse is probably not ready for a cart yet.
You need to do some more ground driving him, and pulling some stuff on the ground, like tires or logs.
You need to also work with him in "pretend shafts" made out of PVC pipe or 2X2's, put the pretend shafts on him and work with that quite a bit.
If your horse is not totally ok with the cart it will be disaster.
You might consider getting him gelded, that would calm him down a lot. You know the saying, "An okay stallion makes a great gelding"
He is still young, Keep ground driving him through the cold winter up in MI, and you might be ready in the spring.
I don't know anyone in MI, maybe you could look for a driving club in your area to learn some information from. MI clubs are listed at the bottom of this page: American Driving Society
As for jumping, it sounds like you have a nice horse. To help keep him nice and his legs healthy, I wouldn't ride a horse till it is almost 3 and you deffinatly should not jump a horse till 4 or 5.
Good luck to you and your horse!