I've been to Japan several times and it's one of my favorite countries to visit. While it's always nice to have a native speaker around, everyone is quite civil there and getting around is quite easy at least in the cities (compared to other countries) even if you don't speak english. The subway system is laid out quite logically and enough things are written in Romanji that it's not an issue.
Things just work there (like the trains). I remember a waitress apologizing at an italian restaurant that our dish would take "8 minutes." Hilarious. It's one of the few countries that feels really safe; you see little kids (like <7) going about their own business riding trains and buses without their parents. I've only really seen that in Munich and (certain parts of) Israel.
It's also the only country I've ever been to in the world where people will stand in a line, patiently, waiting for a taxi stand instead of trying to cut each other off.
If you like cute stuff, they've got it. In droves.
If you like japanese cuisine (more than sushi), it's fantastic. I personally love the whiskey hi-ball and takoyaki combo. Also the different types of okonomiyaki (my favorite is hiroshima style). Other regional cuisines are interesting -- like kushikatsu in Kyoto (basically, deep fried bits of stuff on a stick -- like tempura meets yakitori). Ramen though remains one of my favorite things to eat there -- there are so many regional variations you can literally eat this for every single meal and not have the same one twice.
My best advice if you dont have a direct recommendation is to find a ramen alley (street with multiple ramen shops) and look for the ones that are the busiest.
You probably have most of your trip planned already but if you get the chance:
- day trip to Nara. It's one of the old capitols of Japan. Amazing and chock ful of temples+deer.
You should check out this Cars & Coffee. I haven't been but it's on my to-do list for my next trip.