[MMM]

The more Japanese you know the better, but you will pick it up quickly if you try. Especially in Tokyo, reading isn't as important as speaking and listening. There are a lot of foreigners in Tokyo, which it both an advantage and disadvantage. The advantage is that you can probably find an English-speaker that can help, the disadvantage is that Tokyoites are less inclined to help foreigners than they are in other parts of Japan. A little more independence is expected of you. (Not unlike New York or London or other big international cities).

The biggest worry would be money. It's an expensive place to live, and living like a miser in Tokyo is not only not fun, it probably isn't healthy. Make sure you have enough cash to be able to do this. It's easy to drop a couple hundred bucks in a night if you aren't careful. Sometimes just "visiting a friend" can add up (2 train transfers, 5 bucks a train [for example], then the return trip home...WOW there goes 30 bucks!).