Convenience & Prior Reservations

I'm planning a trip for late autumn this year and looking at our options.

So far it seems that the JR pass might not be quite worth it for our trip (Tokyo-Hiroshima-Kyoto (+ day trips to Osaka)-Nagoya-Odawara-Tokyo (+ day trips)). I have added up the cost of the main Shinkansen legs of ou trip and it comes to around EUR430 each next to a 14 day pass at about EUR550 each. However, I am aware that the JR pass does cover some other local travel...(airport train, some metro trips, ferries etc) which may make the difference negligible. So I have two questions?

Am I right in assuming that having the JR pass is just much easier that having to book lots of individual trips (although I realise we still need to reserve seats)? Klook seems to be the most simple app for Shinkansen tickets...how else would you recommend buying individual tickets - other then at the station?

Also, with regards to seat reservations, we fly into Tokyo Haneda, arriving early in the morning. Our plan was to travel that day to Hiroshima and work our way back to Tokyo over 2 weeks. from what I have read, I assume we cannot reserve any seats before we arrive and activate the JR pass. Can I assume that on a weekday in November, we will easily be able to reserve seats on arrival on a mid morning train - with a train every 15-30 mins I guess that would be possible?

Thanks for any thoughts.