Looking for tips and suggestions, Hokkaido

Its my 3rd time to Japan, and this time round i'm fulfilling a two bucket list in this trip to experience winter when it's snowing and to Ski.

We'll be in Hokkaido for the first time from 16 to 25 december. Below are some questions or worries i have in mind.

1. We've experienced 1-10 degrees when we were in Takayama, how much more layers should we prepare for Hokkaido during this period of travel?
2. Any suggestions if we should stay at two different areas in Hokkaido? minor concern that 9 days might be too long.
3. If we wanted to SKI for two days (doesn't have to be consecutively two days) is it worth staying at the ski resort?
4. If not staying at ski resort, which place should we go for Skiing? and how should we get there?
5. Do we need to pre book anything to be able to ski? like instructors/rental equipment and what type of equipment we expect to rent?
6. Im quite a big guy, would i run into the problem of their rental equipment not able to fit me ?
7. What were some of other interesting experiences you've tried out in Hokkaido?