As for crowd calendars, a couple of comments. First, you can absolutely understand general patterns. I can tell you right now that in 2032 Walt Disney World will be packed during spring break. There are very predictable patterns that are accurate regarding time frames down to about a week, or even down to the day in some circumstances.
Now, within anyone of those specific time frames It gets a little more dicey.
On a day to day basis, actual crowds are going to depend on things like extra magic hours, the park hours, and other things that are fairly predictable, but may change between now and then.
So if I were you, I would be very attentive to the general crowd levels to identify the week that you wanted to travel. For instance the week before Christmas or the first week of January are probably going to be very different and predictably so.
I wouldn't worry about day to day planning yet. You could certainly map out how the day will work it any given Park, but leave open whether that day at Magic Kingdom will be the first last or middle day of your trip.
Once you get much closer, and things like shows and park hours are better known, then you can use crowd calendars to make some estimates. Even then, completely unknowable things like whether it rains or a ride breaks down can swing things substantially day to day.
Honestly, based on my limited experience, I would say that once you've nailed down the time of year you're going, having a good touring plan is way more important then the minor differences park to park. And for everyone who will tell you to avoid extra magic hours parks like the plague, there'll be someone else who will tell you that's fine.
In case you're not familiar with touring plans, those are strategies for how to move through each park once you get there.
Just as an example, you can pretty predictably know that it doesn't make a lot of sense to go to Pirates of the Caribbean at 10 AM, when the line will probably be fairly long, when experience shows that it is almost always going to be a very short wait much later in the day.
Understanding those dynamics make a big difference in terms of getting a lot done and not waiting in lines.
I think I'm pretty comfortable saying the two big hitters in this area are Josh at easywdw and touringplans.com.
Josh has detailed and thoughtful crowd calendars months in advance. He's also a good one to read just to kind of understand how to approach the parks. I think knowing how and why certain things work can be more important than a really detailed plan, that way as things change you can make fairly good guesses about what to do. Josh is good for that.
Touring plans.com is also a fantastic resource. They've got lots of free resources, but they're paid planner for about $12 is a total no-brainer. I'm about as big a cheapskate as they come, and I feel it was money well spent. They are dashboard helps you look at Crowd calendars, crowd levels, specific ride time wait estimates throughout the day, everything you can imagine. And on top of that, an app for dynamical planning while in the park.
I'm top of that they have an automated system that will let you import where you want to go and give you an estimated best tour plans that you can then adjust.
Those two resources should be more than enough to help you successfully plan your trip.
Off the top of my head, avoid mission space, start wars, Tower of terror, soarin, splash Mountain, pretty much any of the coasters... Touring plans.com ride descriptions will also be helpful for figuring that out.