Hi Mel,
Slow down and take a deep breath. I gather you haven't been to Japan yet.
Japan is romanticized quite a bit by us Westerners. I myself did that a lot before I actually came there years later and realized it was different than I imagined. That's not a bad thing, but you may not find what you expected there, so you really want to go there first for a while, see what it's like, then see if you can find a job. If you can find a job, and after living there a few years,
then you might want to think about citizenship.
Like Jkid said, citizenship is a huge issue, and can be a problem later if you need to fly back home suddenly for some reason (sick mother, home finance issues, etc). Speaking from experience living abroad in various places, unless you've sunk roots pretty deep in a country, you really, really don't want to get citizenship there yet.
Now, if you just want to go to Japan, some good advice if you want to succeed:
1. Learn the language!!! Japanese is an especially difficult language to learn, and unless you're willing to put years of effort into it, you might find yourself quickly getting frustrated over there.
2. You need to develop marketable work skills. Teaching English is the easy-way, but I've heard from many that the pay is poor, and you work like a slave, with little chance of promotion. Instead, you should develop other trade skills which coupled with japanese proficiency, would make it much easier to get a nice, comfortable job there.
3. Visit on vacation first, so you can really get an idea what it's like. Culture shock is a really challenging thing to overcome anywhere, and you'd be surprised how hard it can hit. Vacation's are nice way to sample the culture first. Even in English-speaking places, culture shock can be hard, and much harder when it's a non-English speaking country.
...again, all speaking from experience.
Best of luck.
