Shinkansen Okayama - Hiroshima

Hello!

I'm travelling to Japan in April and I have a few questions:

I would like to go from Okayama to Hiroshima on the 10th of April. I think the fastest way is to use the Shinkansen. I have seen that the Sakura Shinkansen travels from Okayama to Hiroshima and is eligible with the JR PASS but I cannot find the timetable and the duration of the journey. Could you please help me?

Another question: On the 9th of April, I would like to travel from Okayama to Tottori, then to Matsue and back to Okayama. Do you think it is Ok in just one day? I cannot find the timetables.

Is it better to buy the JR PASS online or can I buy it when I arrive in Japan?

Thank you very much!

Mary