Advise on 16 days itinerary

Hi!
I'd like the opinion of you if this itinerary for 16 days is doable.
It's my first time in Japan, there is a lot to see but I didn't want my trip to be stressful. I'd love some advise on nice/quiet/peaceful/not-to-crowded places to visit too.

Day 1 - Arrive in Tokyo in the afternoon. Just have dinner and sleep.
Day 2 - Explore Tokyo
Day 3 - Side trip to Mt Fuji.
Day 4 - Explore Tokyo
Day 5 - Leave early to Koyasan. Spend the night at Koyasan.
Day 6, 7, 8, 9, 10 - Kyoto with side trips for Nara and Himeji.
Day 11 - Magome
Day 12 - Nakasendo Trail. Sleep in Tsumago.
Day 13 - From Tsumago to Takayama
Day 14 - Takayama /Shirakawa/Gokayama
Day 15 - Takayama /Shirakawa/Gokayama
Day 16 - Travel no Narita Airpoirt

From day 14 I'm really don't know whether to stay in Shirakawa or in Takayama, or if its worth to go to Gokayama or do a side trip to Kamikochi. Any tips for a nice onsen near Takayama?

Thanks a lot

Going from Tokyo to Koyasan in one go is a long day of transport. Have you considered breaking it up with an overnight stay in Osaka?

Well i disagree. Koya san may take time to get too but the poster is taking an early train. Furthermore, Koya san does not have many attractions to see. it is easy to cover. In fact, the whole idea of Koya san is slow idyllic walks.

For someone who wants peace and quiet, Tokyo would not be a good idea. I recommend spending a night at Karuizawa or Kusatsu. Japanese Resort Areas.