I would say, it might be hard as a vegetarian, but there are restaurants that sell vegetarian meals, and there are places that are compatible to your needs as in, they can exclude ingredients if you ask (but, you have to ask).
Not all restaurants have ingredients written down, so you do have to ask
I don’t like spicy food and sometimes, it’s not obvious, so I end up choosing one meal that I want, but I’m not sure about, and one for back up in case they say it’s spicy.
Very kindly 
If you know a few basic things, you can get around. There is a lot more English around after the Olympics and the big surge of tourists, so, knowing basic will help, but you don’t have to grind and try to learn high-level Japanese at all.
Hmm
I want to say, “oh yes, very chill everywhere“ but then I think of the reality. I won’t say there aren’t any politically radical kind of people in Japan. Tokyo or Kyoto or any of the big cities are generally chill about it though, I would say. You’d be fine 
And people are a lot more accepting than they were twenty years ago, so, that’s good.
Uhh, things have changed a whole lot since I was in elementary school
But if you want to learn how to speak it, just concentrate on that. If you want to learn how to write it, I have heard it’s a terrible process because you need to learn, three different ways of writing
We have hiragana, kanji, and katakana (mainly for saying foreign words). Even in elementary school, you would start with those three, I think.