sounds all great blah blah blah but i hate to be the one to break it to you.. a lot of people i know here in Tokyo came and did the same thing as what you're planning to do.. Aka. Come to japan to be with girlfriends, work as english teachers, and try and get by... For some people it works, but also for a large number, the girls go back to living with their families, and returning to their previous state.. a lot of people on other forums (Gaijinpot.com for one) also speak of similar stories.. I won't go into here, but have a look at some forums before you take the big jump to see what others have to say..
Also, Can you speak any japanese? Can you read/write hiragana, katakana, kanji? If not.. id get cracking on learning some before you come..
Hate to be negative, but maybe its more the truth than anything else.