Which pass to buy, activation and booking tickets

Hi there, I will travel to Japan on 19 Feb. I am Flying onto Kansai Kukoo, travelling straight to Kyoto to see friends, then Osaka and to Tokyo on 24th. I need to travel back to Osaka on the 29th to fly our of Kansai Kukoo again. I just wanted to check what the best pass is. Is it a 14 day pass?

I also want to check that I can activate my pass as soon as I get off the plane to use it to travel to Kyoto.

Lastly, I am a bit worried about catching the train back to Osaka on Monday 29th Feb. I am worried that due to the Tokyo marathon on Feb 28, there will be lots of people wanting to use the Shinkansen. Are there plenty of vacancies at the moment?

Once I am in Japan and can make reservations, how d I do this to ensure I get a seat on a train back to Osaka to ensure I don't miss my flight home?

Thank you, Susan