My daughter and I went last year from Dec. 30 - Jan. 3. We primarily wanted to enjoy the Christmas decorations and experience some old favorites. We stayed at the Swan which was great because it took care of any transportation issues for two of the parks. We went in knowing that it would be really crowded and that doing extras on the spur of the moment probably wouldn't be possible. So, we made our fastpasses as early as the window opened and were able to get all of the rides we wanted (even FOP) except for SDD. We also made ADRs for the mid day so that we could take a break from the crowds and recharge for the afternoons. We really looked at being able to do anything more as improbable.
About a month before our trip, we found out that my husband would be able to join us for part of the trip. I was surprised that I was able to get him most of the same fastpasses that we had. So far, so good.
When we arrived, we spent the first day at DisneySprings and touring the MK area resorts. We so enjoyed seeing all the decorations, listening to Christmas music, etc. For NYE, we had some fastpasses and an ADR at MK. We tried to rope drop, taking the bus from the Swan, but the traffic was insane. As I remember, it took about an hour to finally arrive at MK. The bus took all sorts of routes that I had never seen before but even on those roads the traffic was really slow and backed up. Happily we got there in time for our fastpasses. It was crowded (in fact admission was restricted for a while), but it really didn't impact us. We enjoyed holiday decorations, entertainment and our late lunch at Tony's. We ate on the porch and loved looking at the Christmas trees and listening to the Dapper Dan's as we ate.
We had already been advised not to use ground transportation so we hopped on the monorail to Epcot after lunch. It was about 3 pm at this point and the monorail was empty. We had the whole car to ourselves. So we spread out and marveled at the line of cars completely stopped and stretching as far as the eye could see. We enjoyed additional fastpasses at Epcot and stayed to see the fireworks at midnight. We positioned ourselves at the back of the park so we could easily exit out the IG after the fireworks. They were incredible - I thought the best I had ever seen. Epcot was crazy crowded and hard to move around in as the night went on. It was fine for us, but I wouldn't have wanted to be there with small children.
The rest of our trip was great too. Busy, but not crazy busy. We were even able to get a few extra fastpasses by refreshing in the app. We stuck to our plans, enjoyed perfect weather and had a great time. My best advice is to make good plans, stick to them and avoid street transportation on NYE.
Hope you have a great trip!