Is the JR Pass best for my itinerary?

Hi,
I am travelling to Japan in February on my own and wanted to check the JR Pass is the best choice and confirm which parts of my journey it will cover and which parts i will need to pay for separately. I want to use the bullet train both for the experience and so that I can have the most time possible at my destinations.
Below is my current plan showing the travel from and to with what I think would be the best way travel.

08/02/2020 Narita Airport T1 - Tokyo Trains Station (NEX)
08/02/2020 Tokyo Trains Station - Iiyama (Shinkansen)
08/02/2020 Iiyama - Nozawa Onsen (Bus)

12/02/2020 Nozawa Onsen - Iiyama (Bus)
12/02/2020 Iiyama - Nagano Station (Shinkansen)
12/02/2020 Nagano Station - Yudanaka Station (Nagano-sen)
12/02/2020 Yudanaka Station - Jigokudani (Bus)

12/02/2020 Jigokudani - Yudanaka Station (Bus)
12/02/2020 Yudanaka Station - Nagano Station
12/02/2020 Nagano Station - Tokyo Station (Shinkansen)

13/02/2020 Travel in Tokyo (Subway)

14/02/2020 Tokyo Trains Station - Narita Airport T1 (NEX)

I was also looking at getting the Green Class, but once i have bought the pass are there any additional fees for travelling such as if i was to reserve a seat?

Thanks
Tom