AJapan: QR PASS
You should definitely use your JR Pass for the Shinkansen Kamizawa trip between Osaka and Tokyo. Then, I'd recommend visiting at least Kyoto and Nara Prefecture Besides,...
AJapan: Is the JR Pass worth it for 2 weeks in Japan?
Yes! That's a lot and definitely a good itinerary for the Japan Rail Pass, which is always worth if you go to Hiroshima from Osaka or Tokyo, and back.
ATokyo: 3 nights in Tokyo - where to stay to meet people late twenties?
Shinjuku/Shibuya would be your best options. Great transport - including to/from the airports. All of the other areas you're referring to are a quick train ride away :)