[Hatredcopter]

I'm afraid I don't know when or how competitive applying for JET within Japan is, as I applied from the outside, but I can give you some information about your other questions.

First of all, it's not very likely you'll become a JET in Tokyo - even some of the smaller, surrounding areas (like Chiba) don't take in that many people, but it's still possible. Just out of curiosity, why are you set on Tokyo?

As far as accommodation, JET will help you with that - for ALTs, you usually simply take the same apartment as the ALT that you are replacing, which means you'll have a furnished place. You'll also most likely get the place without paying any 'key money'.

If you have the funds and the time to check out Japan on a WH visa first, I'd say do it. JET is a fairly big commitment, and it always pains me to see people who come over on JET or any other organization and end up hating things because they don't "get" Japanese society. That's not to imply that a lot of them do, but there are a few individuals who obviously had different expectations.