In terms of international travel, I would ask yourself what kind of experience you want with others. Japan is a relatively easy country to move around in if you don't know Japanese, but English isn't universally understood.

I'd recommend taking some English tours at minimum to give yourself someone to talk to in a language to understand.

You also aren't going to be able to see all of Japan. I would focus on a few parts you are interested in instead of trying to see the whole country.