Why do you want to move to Japan? People seem to think it's some sort of utopia for introverted anime nerds, which is absurd. I'm not laughing at your idea, I just want you to be more realistic about it.
Jobs are not easy to come by for any potential immigrant to a developed nation. For one, you can't exactly move there and then find a job, it doesn't work like that. You'd need to find the job first. You undoubtedly won't be able to immigrate without some very impressive credentials and a job offer. The exception to this is teaching English, for which there are bound to be quite a few more opportunities. It would only be temporary, but that's going to be your best bet. Start learning Japanese in some capacity now and look into teaching English abroad programs, their requirements, and approval process. Also, Japan is a very expensive country to live in and get to, so I hope you have extra money. If you did a teaching program it's likely your living expenses would be covered, but you probably won't have very much extra money. It's also likely you won't get to choose where you live in the country.
To your other questions.... Is it safe? Yes. Convenient? Probably, but this depends to some degree on your Japanese proficiency and location. I'm sure as you get further from the major cities what little English the locals know decreases.
Are your reasons for wanting to move to Japan beyond something like, "It's a paradise for otakus like me?" Maybe you just really want to live abroad someday. If so, then I'd recommend adjusting your trajectory a little south toward Bangkok. You'd have much better chances of finding employment, and Thailand has extremely lax visa policies. It's also considerably cheaper in most respects than where you live now, let alone Japan. Hundreds of thousands of Westerners live in Thailand and millions visit every year, so English is everywhere. You shouldn't need to learn much more than Thai numbers, transaction phrases, and salutations, (though you really should.) Oh, and for only a few hundreds dollars you can fly to Japan from there.
Edit - I should add that finding a job in Thailand would by no means be easy. Just that it's more likely for you than in Japan and you wouldn't have to find the job first.