[Firebird]

You can use the Railpass in Tokyo but only on the JR Lines. So if you want to take the Subway youll have to pay extra. I think the JR is better to get around Tokyo but like i said in my post, if you only travel once a long distance it might not be worth it. You could just get one for a week and travel to another city in that week. Transportation inside Tokyo is not to expensive, as long as you stay in the central Area. One Trip was around 160 to ... i dont remember maybe 300yen for a longer trip? Be aware that train stop around midnight and Taxis are expensive!

I would say Roppongi is a little bit like Khaosan road in Bangkok. I personally didnt like it and dont recommend to spend your evening there. The Area is full of foreigners, so lots of bars target foreigners. I got many people trying to get me in their bar or club and some people say that next to Shinjuku this might be the only dangerous place in Japan after the last train left. But make your own impression, everybody is different!
There should usually be some people around the Hostel that will go out some place together at night.

Big citys do get backpakers and all the touristy place will have them as well. If you got to places Like Tokyo, Osaka, Kyoto, Nara and the like, you will find quite a few people at the Hostels. Places like Sapporo or Hiroshima see less backpackers but they exist. Got to Sendai or Nagoya and people will get fewer. In any smaller, less popular places it was rare to meet foreigners.