First time Solo Trip. Need help please.

Hi,

I am in the early days of planning a 1 month(26 days) itinerary for Japan. I am planning to go in December. This is my initial draft based on my research. This is what I have setup:

  • Tokyo - 10 Days
    • Tokyo skytree
    • TeamLab Planets
    • Imperial Palace
    • Shibuya Crossing
    • Shibuya Sky
    • Tsukiji fish market
    • Tokyo tower
    • Explore shinjuku
    • Kuji Temple
    • Explore Akihabara
    • Hie Shrine
    • Day trip to Hakone & Lake Ashi Cruise
  • Fuji 5 lakes - 3 days
    • Staying near Kawaguchiko staton
    • Bike around Lake Kawaguchi
    • Kawaguchiko Ropeway
    • Chureito Pagoda
  • Kyoto - 7 days
    • Fushimi Inari
    • Nijo Castle
    • Kyoto Imperial Palace
    • Kiyomizudera temple
    • Arashiyama Bamboo forest
    • Kiyomizu-dera Temple
    • Day trip to Nara
    • Day trip to Osaka
      • Osaka Castle
      • lambda Yasaka Jinja Shrine
    • Day trip to Himeji Castle & Mt. Rokko
  • Hiroshima - 3 days
    • Peace memorial park
    • Visit Miyajima
    • Explore Hiroshima

This what I have so far. It's a total of 23 days & I still have 3 days left. I'm quite overwhelmed with all the planning required. I could use some help improving this.

I'm looking for help around:

  • Is this itinerary making good use of my time?
  • Am I missing anything important?
  • What are some must have experiences in Japan?
  • What should I do with the 3 extra days (I guess 2, last day would be mostly getting to the airport).

Any help would be welcome. Thank you in advance.