Depending on how long you intend to stay, you might wish to prepare a few packages to mail to yourself in Japan. A package with summer clothes and another with winter clothes, for example. Of course, you probably don't know what your mailing address will be now, but by the time you need the packages, you will know the address. Just leave the packages with a friend or relative and ask them to address them and post them for you.
As far as shoes go, I wear US size 11 (29cm). Most Japanese stores only carry men's shoes up to size 27.5cm. Anything larger can be very difficult to find and the selection is very small.