Trip in October

We plan our 2nd trip to Japan as follows: Osaka (incl. Himeiji) 3 days-Okayama
(Incl.Naoshima) 2 to 3 days-Kyoto 2 days-Tokyo (inkl. Nikko, Kawagoe,Kamakura,
Yokohama) 8 days.
Any other suggestions (we have seen already: Hakone,Takayama, the Alps and
Kanazawa).
Thank you for your suggestions.

Izu peninsula is nice.

If you want autumn colours you might get them at Kamikochi in mid October, possibly Nikko too

We really liked Kawaguchiko. Nice Fujisan views, beautiful kimono museum (the kimono were works of art, not to mention the museum itself), and maybe the momiji tunnel will be red (I don't know when it usually happens). We stayed at Weekend Shuffle and the owner is just great. Took us early in the morning to a private mountain viewing area to see Fujisan. Also in Okayama, if bicycling in rural areas is your thing, you might like biking in the Kibi plains.

you could also do a day trip from tokyo to karuizawa. In october, there should be a momiji festival ( not the type with mikoshi and parades. Haven't been there but will be going in october.

Good thinking. Karuizawa is an awesome town. Nice hike to the lookout and temple, great fun shopping street, good eating, good launch pad for Kusatsu. For a ryokan stay, Tsuruya is excellent. Last time we went we stayed the Le Grand Kyu which is also excellent.