3 full and 2 half day itinerary in Jan

Hi there
I am visiting Hokkaido for a short period this January (23-27) with my wife and 13 year old son. We are visiting during Chinese New Year holidays so will miss main winter festivals in February however would like to make most of our time there by learning Ski 1 of these days (this would be our second time skiing) and relaxing in onsen, enjoying beautiful Hokkaido winter. We have only few days so appreciate expert help 8n planning our itinerary.
Day 1 Jan23: arriving new chitos airport 1.30pm and transfer to Niseko (overnight)
Day 2 Jan24: Niseko ski lessons and relaxing in the area/ onsen
Day3 Jan25: Niseko relax/ ski or onsen or option 2- Niseko to Otaru (overnight)
Day4 Jan 26: Niseko or Otaru to Sapporo - and to Jozankei onsen overnight at Sapporo
Day5 Jan27: explore - odori park/ other attractions in Sapporo half day and leave for airport in the afternoon
Please let me know 1) if this itinerary works,
2) should I spend 1 less day in Niseko to get additional time in Sapporo ?
3) is Otaru worth spending a night? Would there be pre festive atmosphere in the evening around canal?
4) would onsen experience be better in Niseko or Jozankei or any other suggestion per this itinerary.
5) which would be the best resort/ area in Niseko for bigginers ski lessons in terms of English speaking coaches, slops and ease of traveling to and back to Otaru/ Sapporo.
Thanks in advance for your help.
MJ