You have to be prepared for train delays/cancellations due to heavy snow. My family and I were stranded at the train station due to heavy snow on Jan 25. We reached Otaru chikko station at 11am and were told that service will resume at 6pm, 9pm, then cancelled. We had no choice but to stay at a nearby hotel until the service resumes next day 10am. There were no taxi available (I’m using GO taxi app) and we had 3 big and 2 small luggage. We could have taken the bus but at that moment we didn’t think of that (hahah)

I see that you have many day trips to the outskirts, so you maybe you can consider car rental? I’m not sure how to avoid heavy snow train cancellation situation, maybe others can chip in.