Okuri ashi help for kendo?

While everything you mentioned can be a bit of a hindrance. I don't think that your difficulty is coming from the problems with your feet. The problem most likely lies in your technique. Okuriashi is easy to learn and hard to perform. I think you are putting too much weight on your gliding foot. The footwork is meant to teach you how to transfer your body weight from one foot to the other while maintaining posture and a bit of forward balance. Try thinking of it as more of a "push, pull" motion. Driving off your rear foot more, and pulling it in with your front foot once it's planted. Since your new, I would encourage you to work at a slower pace, especially at home. The little bit you do in cl is not going to help you learn it well. Be patient, work slow, and concentrate on the small things. Good Luck