As a general rule, as long as you have a round trip from Tokyo to Osaka (or Kyoto), then a 7 day JR Pass will be worth purchasing. Here are your legs just to be sure:
- Osaka > Tokyo (¥27,100 return)
- Osaka > Kyoto (¥1080 return)
- Osaka > Kobe (¥780 return)
If you add another ¥2200 the leg to or from Kansai International Airport, that would also be covered by a JR Pass and you will save around ¥2000 with a JR Pass (¥28,300), in addition to having the flexibility to go off to other parts of Japan on day trips should the fancy take you.
Recommendation: 7 day JR Pass
Hiroshima, Takayama and Kinosaki onsen are also all good day trips form Osaka you could fit into your holiday.
Hope this helps!