We've done Universal Columbus day weekend, and Thanksgiving. BUSY, but we did have express. Have also done both those holidays at Disney, but we've never done Christmas at either, so that may be a whole other level of busy. It's good you're already expecting that!
I still think rope dropping super early is very important , Like if opening is 8, be in line by 7:00 or so, if you can. We tend to eat at off times, so maybe eat lunch late, like 2 or 3, with a good snack in the AM. We actually try to eat around 10:30 or 11, right as places are opening, and don't have issues, but that may still be prime riding time for you. Crowds do thin out quite a bit in the evening. Wait times are much lower... usually. BUT the Sunday before Columbus day, in the last hour, lines for things like Butterbeer, Hogs Head, were VERY long, and, all stores were packed. We did do Ollivander's that night, and waited about 20-25 mins.
Not sure if y'all have been before? how old the kids are? do they like thrill rides? It's often said that Universal is not like Disney as far as planning. That's true as far as dining reservations at 60 days,
genie+, all of that. BUT it's still very much worth it to do research. Sit down and talk about what everyone really wants to do. We now have 2 teens, and they wanted completely different things, 1 wanted HP exploration, and 1 wanted nothing but rides. We split up! not all day, but some. If there's a ride that nobody really wants to do, like for example, none of us really want Seven Dwarves coaster at MK, so we all know not to waste time there. Also research restaurant menus. So, everyone knows in advance what to expect. And have a backup plan. One morning, Velocicoaster was not running at rope drop, so need to know what everyone might want to do instead, or wait it out, etc. We did enjoy the wand experiences, but most had about 2-4 people ahead of my daughter in a lot of spots. So you might see the spells happening before your turn, or maybe try to just look away, but she still enjoyed it. So glad we finally did the wands.
I do love the Florian's ice cream. The Thanksgiving we were there, Diagon Alley was PACKED. Like we were all holding on to each other's back to stay together, ha. and the florian's line was out the door and wrapped around. I love the more exotic flavors: clotted cream, earl gray, etc. but everyone else wanted butterbeer ice cream.
Hope you have a wonderful trip!! You'll get to be there at an extra magical time for the holidays. Universal does such an amazing job with decorations and holiday touches!