[MMM]

A lot of those questions are "depends" but let me tackle a few of the more concrete ones.

It is probably easier to live in Tokyo and not know Japanese than in other cities just because there is a signifigant nomadic foreign population that doesn't speak Japanese, so Tokyoites are more used to it.

That being said, start studying Japanese today. Every minute you spend studying now you will thank yourself later. Train stations and bus stops have signs in English, but that's about it. Go with the assumption that 99% of the people you meet in Japan won't be able to speak English.

Learning Japanese simply by living in Japan is hard. It's like being thrown into the lion's den with some sheets of metal and being told to forge some armor before the lion's eat you. Again, start learning now. Buy a text book (I'd recommend a real college "text book" rather than a "Japanese in 10 minutes a day" type book. If you were going for a week, that would be fine, but might as well learn the grammar so you can create your own sentences rather than be limited to the set phrases you are taught. I am partial to Youkoso.

Many people start studying Japanese and want to start getting the kanji down. I would learn hiragana and katakana, but focus on speaking and listening more than reading and writing. Especially if you aren't using Japanese for work your need to read and write is about 10% of your need to be able to speak and listen.

Especially when dating. Tokyo is a very modern city. Inter-racial couples are no big deal. They are no big deal throughout most of Japan. It is harder for ex-pat women to find love than men, though. But of all the foreigners I know that lived in Japan, I can't think of one (men and women) that didn't date a Japanese person at some point. A few of them even got married. That's the least of your worries (unless you are morbidly obese...)

Your employer should be helping you with housing, and you probably want to find something close to your work. Do you know what part of Tokyo you will be working in?