Regional Pass or Separate Tickets?

Hello,

I'm planning to go to 12 days trip to Japan this April 2024 and I want to confirm a few things...

My plan is the fist day I arrive at Narita Airport move to Osaka, 3rd day go to Kyoto, 6th day a day-trip to Nara and then the 7th day from Kyoto to Tokyo.

I was thinking, maybe I can a buy a separate ticket to take the Tokaido - Shinkansen line first and then I can use the Regional Pass Osaka-Tokyo Hokuriku Arch Pass for the rest of the trip.

• Should I buy the regional Osaka-Tokyo Hokuriku Arch Pass or separate tickets?
• If so where can I buy separate tickets? Can I buy them online? -Once I buy the regional pass or separate tickets, Will I have access to separate seats and check itinerary?
• Can I have access to itinerary before buying tickets? And where?

Thanks in advance!!!!