OMG! Disney World!!! Can I come??? :P
My family & I just went there last year, March 28th - April 4th. We went on spring break, the second busiest time following Christmas (I believe) and it wasn't bad crowd-wise for us at all. If you know how to use Fastpass, it will make things sooo much easier and the waits so much better. We never waited more than an hour if I remember correctly, which is great for the time we went.
Do you plan on staying onsite? They have a lot of resorts/hotels broken into three categories- deluxe, moderate, or value (most expensive, moderately priced, least expensive). We stayed at Port Orleans Riverside, a moderate resort and LOVED it. I strongly recommend it, but whatever floats your boat! There are many advantages to staying onsite...its more of the whole Disney experience first of all. Also, the best part, you get bus transportation from park to park and back to your hotel, etc. The transportation system there is amazing. Also, if you stay onsite and fly in, you get to take advantage of Magical Express - a Disney bus that takes you from the airport to Disney World, and vice versa when you go home, for free, so you don't need to rent a car or anything.
I also suggest using Disney's Meal Plan. It's sweet. You get way more than enough food every day and my dad said that we saved a ton of money that way.
My parents planned far in advance too. Of course plane tickets will be cheaper that way, and you can take your time planning where you want to eat (I'd strongly recommend reservations, we did this and it worked out great...just ask the family where they want to eat), what you want to ride, etc.. Our tickets were a great deal, we flew United with a layover in D.C. and then onto Orlando. Wow, I am feeling nostalgic just think about it!
We also got the parkhopper pass- it means you can go from park to park anytime any day. That was great, because if we wanted to ride something in, say, Epcot and we were in MGM we could just go to the bus area and hop on. I'd definitely get the parkhopper pass. : )
I don't even know how to continue or what to touch on...WDW is AMAZING. I cannot wait to go back. So I'll just give some of my favorite rides and restaurants, things I think you should try out! : P]
Rides (with park they're in)
Rock n' Rollercoaster (if you like thrill rides, this is unbelievable) - MGM
Tower of Terror (how can you not?) - MGM
Space Mountain - MK
Splash Mountain - MK
Test Track - Epcot
Mission: Space - Epcot, there is a mild and wild side. My dad and I did the wild side. Warning: not for the little kids, this ride (the wild side) actually has sick bags inside. You were warned....; )
Soarin' - Epcot
Expedition Everest - AK
Buzz Lightyear something-er other - MK (this is something the whole family should enjoy)
Mickey's Philarmagic (3-D show) - MK
Big Thunder Mountain Railroad - MK, roller coaster but not too scary or anything
Disney's Beauty & The Beast (show) - MGM
Killimanjaro Safari - AK, we didn't do this unfortunately, but I've heard it's a must see
Pirates of the Caribbean - MK (come on, you have to!) especially with the Johnny Depp!
The Haunted Mansion - MK, a classic. Seriously, if one goes to DW one must ride this. It was recently refurbished too.
Hall of Presidents - MK, a cool "show" (sort of) of presidents who talk - they're all um, some type of robot thing, animatronics?? IDK, but the technology in this is pretty neat.
Epcot's World Showcase - not a ride, but like half of the park...we didn't do a lot here, but next time I can't wait to. You must let me know what it's like when you go!
Studio Backlot Tour - MGM, this is sooo cool. It takes you "backstage" in an action movie, showing how they do certain scenes. You'd really have to see it to get it.
'kay enough rides... Can you see how much I love this place?
Restaurants, this is getting long so I'll just list the places we ate that I recommend:
Hoop-dee-doo Revue - show/food. LOVED IT. I can't wait to see this again! It was really funny and entertaining for me.
1900 Park Fare
Coral Reef
Ohana
50s Prime Time Cafe
Drive-In
Planet Hollywood (tho this is in Downtown Disney)
Sci-Fi Dine In
Spoodles
OH, and you've GOTTA see "Wishes" the fireworks show in Magic Kingdom. This was beautiful, with the fireworks and music. Definitely something the whole family will love, assuming none of your kids are afraid of fireworks (when I was younger I used to hate the noise) lol. "Illuminations" at Epcot is breathtaking too. You just have to see it - you'll get the magical part of it all right then and there.
Wow. I could write a lot more. But I won't. :D Have fun!!!!! I know it's probably a ways away but still! .. oh, and take advantage of the Photopass. You get pictures taken by employees for free in prime locations - Cinderella's castle, MK entrance, etc. and you can look at them online when you get home and order any you like.