Already Traveling

Hello.
My partner and I are already traveling and are currently in Vietnam for the next two and a bit weeks before heading to Japan. So this is really two questions:

We were thinking of getting the 21 day Nation Wide rail pass for our visit (we are planning on visiting for a total 25-30 days). We aren’t quite sure yet what we plan on doing but we’ve currently got a week booked in Tokyo and the only other things we for sure want to do is go to Osaka and Kyoto. But we like the flexibility of going other places the rail pass might offer. Is the rail pass the best idea for us or is there another pass (or passes) we should go with?

Is it even possible to get the pass if we are traveling at the moment? Is there a way to get it online? Can we get shipped to our AirBnb in Japan?

Thank you for any help 🙏🏻