I'm not sure what to add but here goes. I would not worry about things being too crowded as even if it is busy not everywhere will be and Japanese crowds are very polite.
Firstly a little about me. I am British, 55 and have been to Japan 8 times, most recently in March/April this year. I am interested in most things from anime to history & modern culture. As you might imagine I have visited all the places on my itineraries.
So, a little more detail, let's see. I prefer not to move about too much but to base myself in a place and day trip so I'm not always dragging my luggage around. I think that my suggestion has a balance of cities & countryside and offers a chance to move days around to fit the weather.
Tokyo: Sensoji, museums, Ameyoko, Akihabara, Meiji jingu
Nikko: I found it a little overblown but a perfect day trip
Kanazawa: A nice town but you can see the good stuff in two days at most. Of course the main draw is Kenroku-en and the samurai quarter which is great. However I particularly liked
https://www.kanazawastation.com/kanazawa-shinise-memorial-hall/Kyoto: There is so much at Kyoto you could spend all your time there. Nara & Osaka are very easy day trips. I might skip Osaka but not Nara for the giant Buddha & deer park. I like Hikone as it is a bit off the trail, has an original castle & garden. I really liked the museum of the Ii family. However the hidden gem for me was Ryoanji with it's stone garden like the famous one in Kyoto. I was the only person there during my visit.
http://www.ryoanji.jp/smph/eng/Kinosaki Onsen: Not been here but its on your itinerary
Hiroshima: A fabulous place, so much to see. and eat :) Having a few days means you can be sure of a good day at Miyajima (Check the tide times). I found The Battleship Yamato museum at Kure very interesting & great for a wet day. Takehara has an area of preserved buildings & is a very pleasant wander. Here is someone else's travel report
http://www.japan-guide.com/community/pby/report-1989Okayama: I love this place. It is a good honest Japanese city that is not overrun by tourists. The main attraction is the Korakuen garden. But it is a great base for day trips. You can hire bicycles & ride the Kibi plain or take a ferry to Naoshima for the modern art. I hiked up to Bitchu Matsuyama castle in September & it was unbelievably hot but I saw so much wild life. I stumbled across Raikyuji temple & that was superb.
Tokyo: Stop at Himeji castle on the way. The garden next to the castle is also worth a visit even though it is modern. Shopping frenzy!!
Hope this helps. The destination guides on this website are a great planning tool.