Wondering if pass is worth us buying

A group of us are flying to Osaka, heading to Kyoto, then training to Nakatsugawa to do the Nakasendo walk. There is a train trip in that going from Tsumago to Kiso-Fukushima.
We will then heads to Tokyo by train - and leave from Narita Airport.
We will be in Japan for 2 weeks - Is it worth our while buying a pass - is the pass suitable for all train trips? I have never been to Japan before - would love to know the best option for us please