if you plan on travelling around japan, get a Japan Rail Pass; it's awesome, cost about £200 when i went; but you save so much more that that ^^
I'd say seeing parts of japan other that Tokyo is WELL worth it, i saw Kyoto, Osaka and then Tokyo, Osaka was good 'training' for a larger city, and was good fun too.
Good tip for Tokyo, look for hotels in the less touristy parts of Tokyo; they're cheaper, but still just a easy to get about to / from. The Tokyo subway system is awesome ^^
don't worry too much about not speaking Japanese, but
do not rely on people knowing English, really not that many people will. if you try then they appreciate it ^^ I often ended up going into a shop and the people would go and find someone who could speak English for me, even if they were from a rival store; it was really sweet
Even if you don't learn much Japanese before you go, yo will learn some while there; i certainly mastered how to say thank you and excuse me / help! (I can't remember anymore, i have problems learning languages
)
gods, i wrote an essay :P sorry ^^
edit: also i used
this guide for greater japan; it's really good ^^