Using the JR Pass to book tickets

Hi there

I've just got a few questions using the JR pass to book Shinkansen tickets for my holiday between 27/08/14 to 03/09/14

1) I want to travel to Hiroshima from Tokyo on 28/08/14 but on a day visit (going to the Peace Museum)--now I understand that I would have to travel early morning from Tokyo so that I could return in the late evening but please could you tell me if I should activate my JR Pass when I arrive in Tokyo on 27/08/14 and then immediately book my return tickets (Im travelling with my wife) for Hiroshima or shall I activate my JR pass for the 28/08/14 and then go to Tokyo train station in the early morning of the 28/08/14 and just get my tickets then.

2) I'm also planning to go to Osaka the following day on 29/08/14 again for a day visit (going to the Kaiyukan Aquarium)--now would it be easier if I just booked the Hiroshima and Osaka tickets together or would that be confusing.

3) Also when I do book the shinkansen tickets is it fairly straight forward--what I mean is that would the staff be bi-lingual or would I have to learn specific Japanese phrases to book the tickets

Sorry for the long essay and I would appreciate any help

Naz