How can I choose a shoe for best leg and foot support?

Couple of things. You want a shoe that has a good arch support built into it or buy an over the counter support to help it. For maximum support try a high top shoe that goes over the ankle. Timberland hiking boots do great.
Depends. Depends on the diagnosis. If u have ankle instability or has foot drop, then a high cut shoe is better for better ankle support.