3 weeks in Japan

Hi

There are four of us and was thinking roughly to follow the 23 days itinerary approx Dec 9th to 1st Jan from this link
https://www.jrpass.com/forum/topics/itinerary-check/posts/three-weeks-in-japan

stating:

Days 1 - 7 Tokyo (with day trips to some or all of Nikko, Fuji and Yokohama)
Day 8 Takayama
Days 9-10 Kanazawa
Days 11-13 Kyoto
Days 14-15 Hiroshima
Day 16 Beppu
Days 17-18 Nagasaki
Days 19-22 Osaka (with a day trip to Nara and/or Mt Koya)
Day 23 Travel back to Tokyo

was wondering if the itinerary is feasible for winter?

Are there any possibility for self-drive or is it better to stick with train?

We did a self-drive in Hokkaido back in Dec 2010, mainly Sapporo-Otaru-Niseko-Rutsusu, car was equipped with snow tires but there wasn't heavy snow back then. Thus was wondering can snow tires withstand heavy snow should it arise?

We have also done Hakone, Osaka, Nara, Kyoto on that same trip. How can I replace these places from the above itinerary?

Many Thanks