Do I need green pass during Obon

Hello, my itinerary is as follows:

03-Aug Arrive Tokyo Haneda
04-Aug Tokyo
05-Aug Tokyo
06-Aug Tokyo
07-Aug Tokyo
08-Aug Tokyo -> Hakone
09-Aug Hakone -> Hiroshima
10-Aug Hiroshima
11-Aug Hiroshima -> Kyoto
12-Aug Kyoto
13-Aug Kyoto
14-Aug Kyoto
15-Aug Kyoto
16-Aug Kyoto
17-Aug Kyoto -> Tokyo Haneda (5:40pm departure).

Question:
1. If I purchase 14 day pass, I assume I should activate it on Aug 4 so I can use it on my Kyoto->Tokyo ride on Aug 17?

1. On Aug 17, I'd like to take the 8:33am or 8:56am train from Kyoto to Tokyo. I'm worried about Obon and my ability to book seats. Will I have problem booking seats if I book early (say Aug 4)? Do I need to get a Green pass to ensure better chance of seats? We are two adults and 1 child.

Thank you.