Practice, practice, practice. And definitely check out this book, lots of great info:
http://www.amazon.com/Understanding-Exposure-3rd-Edition-Photographs/dp/0817439390
+100 to this. Really helped me a lot.
As to Sony and their mirrorless cameras, while sony isn't my first choice for a DSLR the Sony mirrorless is getting some great reviews...
I can't comment on mirrorless, I'm married to my DSLR's and cannon type lenses for them. I'm not switching any time soon that said-
PRACTICE!!!
The first time I went to WDW with a DSLR I only had a few weeks of experience with it. Wow was I behind the curve and I did a lot of "pixel peeping" with the screen to make sure my shots were ok.
You get a DSLR (or mirrorless equivalent) to be able to really capture those hard to get shots you wouldn't get with a PNS or cell phone camera, using the camera on AUTO can be easy but getting into difficult lighting conditions and AUTO can really put you at a disadvantage. *Yes sometimes even a stopped clock is right twice a day and I know how super the new android/iphone cell cameras are, my wife and I have them, the joy of a DSLR/mirrorless is consistency, IMO anyway.
Experiment in Manual mode a lot.
Take shots with the sun coming into your subject from all angles... take shots with back lighting, at night, with lights try and recreate a lot of what you expect to find at WDW.
Also, when you are in a queue, experiment taking shots of things. Figure out your internal flash and what it can and can't do. Consider something to help it, because there will be plenty of times when it won't be enough or will just make things look awful.
For me, the only thing that worked was time and practice. I can now look at something and know about where my settings have to be and be pretty close, if not spot on.
Learn your light metering but realize if you are simply lining it up to line it up, you might as well be shooting in an auto mode, so basic you learn when to trust it and when not to.
Learn to use your spot focus vs averaging so you can get crisp shots of your family and the masses behind them blur out.. when appropriate. Also realize you can't hand your camera off that way to a CM to use because they might spot on something 20 or 200 feet behind you and you'll be out of focus.
With all that practice, you will learn something just as important... what all those buttons and menus do so that when you need to change something, it's second nature and you can do it in a split second instead of missing the moment because you were trying to change a setting and staring at the camera/menu instead of getting the shot.
Also, your second trip with it will be 10 times better than your first and don't live your entire trip thru the viewfinder