Hi Daniel,
During the winter holidays is a beautiful time of year to visit Walt Disney World! My family and I have visited during the last week of December, and it does tend to be a very popular time of year. Many people have vacation time at this time of year, and enjoy spending it at Walt Disney World. You have already done many of the things that I suggest guests do at Walt Disney World at this time of year, including planning to make
Disney FastPass+ selections, and securing some
Disney dining reservations. Let me offer you a few other thoughts for a great winter holiday vacation at Walt Disney World.
I suggest that you arrive early to theme parks, even 30 minutes or more ahead of opening time. Even during this busy time of year, many guests like to sleep in, and you will find the theme parks at their least crowded early in the morning. This will mean that you can get in more attractions at this time. Along those same lines, I suggest that when you do make your Disney FastPass+ selections, that you make them for mid-morning. If you arrive early and experience a few attractions before your first Disney FastPass+ selection and then use your three pre-selected Disney FastPass+ attractions, this can maximize the attractions you experience. Once you have used all three of your pre-selected Disney FastPass+ choices, you can make another, and once you have used that another, again and again throughout the day based on availability.
My family also likes to leave the theme parks and head to resorts for the later afternoon and evening. The resorts are decorated beautifully. One of our favorites is Disney's Grand Floridian Resort & Spa, with an amazing and huge gingerbread house. We will make a dining reservation at that resort and simply enjoy the beauty.
I hope these thoughts are helpful for you, Daniel!