Most Japanese people have a good English vocabulary, but have no chance at forming or parsing an English sentence in real-time. That said, people who have been in Japan for a while tend to underestimate the English skills of Japanese people.

I think you'll be able to "get by" with English just as you would anywhere else in Asia. Definitely in the Tokyo and Kyoto areas, at least, since they are very used to non-Japanese speakers.

The main differences with other parts of Asia: Japan is not as desparate for foreign tourist money, and people are generally more introverted here, so you will not find random people approaching you in English wherever you go.