Wow thank you for all the info folks! So many useful bits that will make our vacation :-::-::-::-::-:! I hope you will bear with a couple more follow ups:

1. New parameter: went ahead and booked the Hyatt Regency Shinjuku (King + complimentary extra bed so it's as close to the Hollywood twin as i can get) as i didn't want to get stuck w a 2nd choice if i waited. Looks like NYE is super super peak even for locals. So we're all travelling out of Shinjuku station it seems.

2. Gala Yuzawa looks great for what we plan to do: just play in the snow, ski lessons optional and the distance looks good. The snow monkey place looks interesting but for the distance and convenience i think we're good with Yuzawa.I assume the spa is traditional Japanese (nekkid?). Question though: Would we be able to do similar snow activity in the Fuji/Hakone area instead so we hit 2 birds?

3. Will do Osaka things for the one day free we have there and Kyoto from Tokyo instead. With this and Yuzawa planned, will a JR pass now be convenient?

4. This being peak travel time for locals, how good an idea is it for us to be travelling in and out of Tokyo? Will we have to pre-purchase train tickets to avoid running out of seats?

5. Any suggestions for me to pre-book in the Shinjuku are for family dinners around New Year's? I want to make sure we can eat and not have to do combine take-out on a holiday .

6. Transpo-wise: Pls correct me if i'm wrong but we do Shinkansen from Osaka to Tokyo Station then transfer to Maihama to get to Disney. From Maihama, Shinjuku (or the station below the Hyatt Regency) is also an easy transfer? Doing Takuhai all the way, of course!

Once again, thank you for all the input!