Hi, I apologise now for the length of this I am Disney mad!
We took our son (5) on his first Disney holiday October last year (2013) for 2 weeks and starting to save to go again (very excited but will take many years) so hope I can help.
If going for 2 weeks and not wanting to take children out of school id go at Easter as it will be less busy and weather will be better for the littlies but be prepared if your wanting to do universal studios, Busch gardens, seaworld ect it is a jam packed holiday we were out everyday and there is so much we didn't do.
So as you probably know Disney has 4 parks;
Magic Kingdom - We spent atleast 4days at this park, using fast passes on one day to meet princess' with hour long queues. We had lunch with Winnie the Pooh and friends here at the crystal palace which was beautiful. Make sure at night you don't miss the electric light parade, fireworks over the castle and the light projection show on the castle. They also do a parade down the main strip every few hours during they day. We also loved the card game you can play here. You get the starter set from a stall (free) next to Tiannas secret garden where you meet her you then go on a hunt around the park saving Disney characters from villains finding secret screens where your magical powered cards fight. We easily could of spent days doing this and not many people know about it plus a great way of properly seeing all of magic kingdom.
Animal Kingdom - We found that Animal kingdom had a more relaxed calm atmosphere so used this park as abit of a chill out day. Make sure to get you Wilderness explorer book from the stand when you get into the park. This is full of tasks around the park for the children to collect there badges (from the film Up)
Hollywood Studios - Lots and lots of characters to meet here! And of course not forgetting the Fantasmic night show which is AMAZING!
Epcot - My partner loved this park exploring all the different countries at the all around the world but son wasn't as thrilled with this park although you can meet lots of characters here and it had the smallest queue to meet Mickey and Minnie. Queues for characters can get ridiculous. At night they have the Illuminations which is a fantastic firework show, fireworks at home will never be the same.
Then there's 2 water parks; Blizzard Beach and Typhoon Lagoon my only tip for these would be get the children water shoes. The floor can get very hot and is rough on little feet.
Downtown Disney - Lots of shops, restaurants, Cirque du soleil are here which was fantastic and Disney Quest a huge arcade like attraction which our son loved. We got reservations for the T REX restaurant here which was great pricey but so worth it.
In terms of when to book just keep your eyes peeled they do bring out some fab deals that can save you hundreds. We booked through Thompson which at the time was the cheapest deal. Floridatix are great if buying park tickets separately.
In 2 weeks for spending money including all meals (we didn't do the disney dining plan) bits for the kids and us! we spent very close to £2000 but we didn't have any restrictions as that could be your only trip to Disney.
We stayed at the All star Movie Resort. One of Disney's Value hotels but we loved it and will definitely be staying there next time we go. Plus the amount of time you actually spend in your room I personally don't see the point in spending more than you need to. This hotel is overly themed they have 5 themed buildings; Dalmatian, Toy story, Fantasia, Mighty ducks and Love bug. Which have huge statues outside my son loved it. And 2 lovely pools if you do need a break day. This Hotel does have very mixed reviews on Trip adviser but honestly it is lovely and clean and staff couldn't of helped us more.
Advantages for staying on site are the free easy to use busses to the parks which really did make things so much easier,
They now do magic bands, you all have your own these have you park tickets, room key, fast passes (if you get the my Disney experience app on your phone you can do your fast on there. a lot easier than it sounds) when pictures are taken with characters the photographer can scan them onto your band and you can also have a credit card put onto these so you really don't have to take things out with you. Staying on site also means you get the extra hours.
With staying on site you also get the free magic bus from and to the airport which means you really don't need to rent car. We did but for the price it would of been a lot cheaper to just get a taxi to universal studios ect.
All Show times, parades and character greet times are on the back of park maps.
Also in terms of the magic bands which I wish wed of done when I said about photographers scanning photos onto your band, go over the top with it they have photographers with characters, infront of the castle, tree in animal kingdom ect you can go and look at these photos and have just the odd one printed for a price if you want to or what we did is when we got back purchased the disk with all the photos on. This is a set price but it means you could have a thousand photos with all of you in them. Plus it saves you having to snap away and just enjoy the moment of seeing your children meet their favourite characters. The photographers are fab and get lots of shots. I was so pleased she caught a photo of Rapunzel kissing my son on the cheek because I missed it!
For the long flight we bought a trunki and filled it with new little bits (colouring bits, new game for leap pad ect)that he had now idea about so that really kept him entertained.
Pack light because you will be bringing lots home!
Most importantly just relax and enjoy it :)
If you miss bits its an excuse to go again haha xx