What do you reckon of my vague itinerary?

Hi there! My partner and I will be travelling to Japan for 21 days for the first time in January (just worked out best with our unpredictable work lives). Im finding planning this trip quite daunting as we've usually travelled to Europe or south east asia, where I feel information is a bit easier to sort through.

Anyways, I would love if you guys would have a look at my very vague trip itinerary. Feel free to add some places to go, suggestions of what to do in these places, or suggest places to go instead of what's listed.

Tokyo (7 days)

Stop in at Fujinomiya for lunch on the way to Kyoto

Kyoto (2.5 days)

Osaka (4.5 days)

Shiga Kogen (4.5 days) we really want to fit a little skiing in, have done my research and defo want to go here.

Back to Tokyo for flying out (3 days)

Please give any and all feedback, desperate for recommendations.

Thanks so much! Much appreciated.