My last farrier whacked his heal all off to we're his frog was hitting the ground and caused a bacteria infection.
I don't know about the bacterial infection, but it is actually IDEAL for the frogs to touch the ground. That is what they are made for.
I agree his feet look too upright now, but I also had a friend with a walker who was clubfooted. So I have seen a walker with feet like that. However, if that is not normal conformation for your walker, I wouldn't encourage clubby-ness.
It is kind of normal for them to have difficulty cantering. I think many of them are never taught to canter under saddle. I have an 18 yr old Fox Trotter who has a heck of a time cantering. We still do it for fun, but it sure isn't pretty. She is pacing, cantering, and doing some of each at the same time. It's pretty weird. I agree with the person who suggested cantering up a slight hill. My mare canters the best on a slight hill (and in a straight line). It encourages them to get their hind end up underneath them for a proper canter. Otherwise they get strung out all over the place on flat ground and you get all kinds of weirdness.
Oh, on the rigging, you know, I think it has to do with saddle fit more than anything else. I just bought a full-rigged saddle (like a roping saddle) for my Fox Trotter and she moves better in that than her old saddle with dropped rigging. But the old saddle was too wide and this one fits, which makes a world of difference. I would think Dixieland would give you the right rigging if they know you have a walker. Gaited saddles is their specialty. I have thought about ordering from them in the past but never have. I did see one of their saddles in person though and thought it was very nice quality.