Hi there,
If you purchase a JR Pass then your cost will be a fixed rate of the cost of the JR Pass. To get to Kawaguchiko, the easiest way is to take a bus from Shinjuku Expressway Bus Terminal - this is not included in the JR Pass but the bus fare is relatively cheap.
I would recommend purchasing a return ticket so that you can then take the Tokaido Shinkansen from Tokyo to Kyoto. Kyoto to Nara and back is accessible via Miyakoji rapid trains which run at intervals of about 30 minutes. Kyoto to Osaka is done via HARUKA limited express service. Osaka to Hiroshima is directly via Tokaido-Sanyo Shinkansen services.
Hope this helps!
Alexis