Height really doesn't matter. I rode a 14.1 Morgan horse and we competed 2' and schooled about 2'3" or 2'6". She could free jump (no rider) up to 4'.
Secondly, you will want to get him used to balancing under an English saddle. When he can do that, walk, then trot, then canter over poles. Not just a pole, do courses of poles, grids, bounces, related distances, etc. after about one or two months of pole work, bump things up to 6"-12" and repeat. Move up slowly at first, especially as your horse learns to find the distance to a fence.
"I'm just sort of derpy sometimes. But that's okay, cause my horse is derpy too. So we balance each other out! ... Right?"