The past 10 years my daughter (now 23) and I have enjoyed several Disneyland vacations. (We are West coast dwellers) Once I planned that first trip, the subsequent trips were easy peasy.
Now we want to finally conquer Disney World. (A family celebration of sorts

) Oh. My. Stars. So many details! I've listened to the Dis Unplugged for years, so I'm not unfamiliar with what is needed for prepping a WDW trip, but still. I find myself seizing up at figuring out the details when I have so much else going on right now.
Yay! I was in the reverse position just last summer, as I took my mom to DL for our first trip there, and we are WDW veterans from way back. I'll try to reverse some things that surprised us about DL that are different in WDW.
1) More travel time everywhere you go, even within in Magic Kingdom. Not going to lie, DL was so much more compact it's crazy. In MK everything is spread out so there is more walking between attractions, and as you probably know, there are more attractions jammed together (not in a bad way) in DL than there are in MK. So, you'll usually walk more in WDW. Also, park hopping takes longer. Some don't recommend park hoppers for WDW but we absolutely love them. One huge advantage is that you can begin and end a day in different parks, just like in DL, but it will take time to get from one to the other, so figure in your travel time.
2) You really do want ADR's if you think you want to try a restaurant. The TS are a bigger deal in WDW than in DL. But, you can indeed get good food at QS locations as well. TS takes up more time, but it also gives you a bigger break in your day. We eat a TS about every other day, and QS the rest.
3) Rope drop is a bigger deal at WDW. If you are early risers, it is worth it to get to your park at least 30 min early (if you are rope dropping Flight of Passage (FoP) at AK, or Slinky Dog Dash (SDD) at DHS, then you can plan to be there around an hour early (at least right now). We attempted rope drop really early at DL and we were the first in line with no one else around, it was nuts to us! lol
4) EMH works different, so just keep track of the hours for each park for each day of your trip. And, be aware they can change them up on you.
5) During your dates EPCOT's Flower and Garden Festival should be going on (if the dates hold true from this year), and I think EPCOT is at it's prettiest then. There are also extra food booths and demonstrations.
6) If you study one thing here on the Dis, make it how to effectively use Fastpass +. Look at the "refresh strategy" threads, and the FP FAQ's.
Two things we have settled on:
1. Stay at Pop (unless we can get a good rate at POR)
2. The week of March 2 -8, 2019.
I love Pop and POR both. Pop is "busier" with more "in your face" Disney themes, good variety in their food court, and POR is more laid back, also a good food court as well (they have a TS restaurant there too). POR would offer you the boats to Disney Springs if you are interested in that.
We won't worry about adding on dessert parties and the like for our first trip. At least not at this point.
I've done the World of Color dessert package at DL, and the Candlelight Processional dining package at Christmastime at EPCOT and those are the only 2 I've ever done. So, I don't really have any advice there. I think you can get along fine without them.
Suggestions on what to do next? We don't know which park to do when, but we would like to start with the Magic Kingdom. Is there a 'best' place to research this type of thing? Google told me to quit bothering him and ask someone else.
Suggestions? Words of encouragement?
I don't ever trust crowd calendars except if it is an actual holiday. How we choose which parks which days; we look at hours and EMH offerings (when I go I'm a rope dropper, so the hours are important if I want to sleep in later or get up really early, also as a park hopper, I can rope drop an EMH park, do what I want, and go to a less crowded park afterward), we decide if there is anywhere we "must eat," and what we must absolutely get to ride. Also, I figure out which parks I would like to start and end my vacation in (so that sets up your first morning and last evening).
Hope you have a ball! WDW is different than DL, but they both have pro's and con's, I love them both and am so glad to have been to both coasts.
Don't get overwhelmed! I think with your experiences at DL, you are in good shape to tackle WDW. Yes, it takes a bit more planning... and the place is BIG! lol But it'll work out. The unofficial guide would be a help, I got one for DL when we went and was glad to have a compendium at hand.