Hiroshima, Osaka, Kyoto, Tokyo

I'm going to be in Japan from 3/30 to 4/7 for the cherry blossoms, and am debating if I should get a JR rail pass. I land in Tokyo on 3/30 at 9 pm, would I have difficulty getting a hostel in Asakusa because of the late time?

What's the best way to go to Hiroshima and the fastest? Please help.

Shinkansen Nozomi is around 4 hours from Tokyo Station to Hiroshima with 8 stops in between. Price is 18550. The Shinkansen Hikari is 18050 and takes an hour longer. You can not use a JR Pass for Nozomi. A 7-day JR Pass is 28,300. So, by using the JR Pass and using the Hikari, you can save 8,800 and that's just going to Hiroshima and back with no side trips. It will cost you 24,000 yen or more Tokyo to Hiroshima, if you decide to stop in Osaka or Kyoto.

Yeah, the JR Pass is worth it, if you don't mind going just a bit slower.

It depends on whether or not the hostel has a curfew and whether or not you will be able to make it through immigration and customs in time. The last train to Tokyo is a Keisei train that leaves at 10:41 PM; connecting at Aoto station to a Asakusa Subway Line train brings you into Asakusa station just past midnight. You may wish to consider looking for a business hotel or hostel en route with a late/no curfew.

For example I just looked up a hostel in the vicinity of Narita Airport:
http://naritaairporthostel.hoteru.officelive.com/default.aspx

Toyoko Inn also has a business hotel with shuttle bus services that run every 15 minutes in the evenings until 10:45 PM.
http://www.toyoko-inn.com/e_hotel/00037/index.html

As Geogeek said, you should use the 7-day JR Pass which will be cheaper for a round-trip between Tokyo and Hiroshima alone compared to regular tickets... just as long as you complete the round-trip within a 7-day period.

FYI, Hikari services are generally split into two sections so you may have to change trains somewhere along the way to Hiroshima. From Osaka to Hiroshima you can just use one Hikari train. But from Kyoto to Hiroshima you'll have to change either at Shin-Osaka or Himeji depending on the time of day; the exception is that there are a few Hikari trains in the morning that run from Kyoto to Hiroshima with no train changes necessary.