I only lived in Japan for a month, so I can't help with all your questions, but first thing is, if you speak English, you will definitely be able to manage just fine.
Not everyone speaks English, but Japanese people are really nice and helpful. A lot of people will definitely help you out if they see you're from somewhere else and you need help, so no worries! I hope you'll enjoy your time there, I'm quite jealous to be honest.*<3