Wow, sounds like a great time. Be sure to take lots of pictures and video. We found autograph books are a good way to get them to aproach the charters. Unless your trip is 10 days keep in mind you won't be able to do it all (that among other reasons is why people like us keep going back.) Also one of those spining light toys helps to break the ice too and give them something to do at night. If you dont' use a stroller now, you might there. I read the average person walks 40 miles in a week at WDW, most 4 years olds can't do that.
If your daugher loves princess, (and who doesn't?) try to get her in at Cinderellas Royal Table for breakfest. (this can be tricky, we have not done it yet because of difficulty getting in.) If you can't, don't fret. 1900 park fare has a great dinner buffet at GF, the food is really good and Cindy, Prince Charming, FG and one mouse is there too. Also Epcot has a princess breakfest at Norway. While you don't always need PS for every meal, I recomend them for these, get them before you leave. CRT 60 days to the day when you leave, start calling at 7:00 am, they sell out before 7:10 I heard. We ate lunch at the castle one day. We didn't have PS, just asked around 11:30 to get it when it opened. We did and had a lovely meal, we even saw Cindy herself in the waiting area. DD was isn awe. Infact we felt this Cindy was much better then the one at dinner at 1900 park fare. She spent more time talking to DD.
We like the all you can eat dinner at Epcot the land pavlion (Garden Grill) Everytime we have ate there Mickey, Pluto and chip and dale have tons of time to spend with us. You won't need those PS until you get there, sometimes even walk up (or call a few hours before.)
If you DD needs to see Airel (ours always does.) The only place to do that is at Fansty Land, Areils grotto. Try to get there early to avoid lines, but it opens at different times, depending on the weather. Ariel doesn't come out if it is too chilly (those sea shells only offer so much protection from the cold.)
Make lots of time for swimming, just hanging out and enjoying the more quiet "free play" areas of the parks and resorts. (Tom sayer island, playgrounds ect...) Make sure you do at least one water park (if not both) they have some great stuff for young kids, but DD liked BB better. If your child doesn't mind being splashed in the face TL isn't bad. Start off slow on the rides, don't take her on Huntated mantion or Priates until you see how she does on other rides 1st. Once scared kids don't want to try new things. At MK hit FL 1st, make the rounds and then leave before it gets too busy (around 10:30.) Use fast pass. Don't try to wait in 45 min lines to see pooh with a 4 year old, that can really wear on everyones patience.
If you DD is old enough to skip naps, she might still need them there (especailly if you wake early to get to the parks before they are busy.) If not a nap, at least back to the resort for a swim and break really helps (if you are staying on prop.)
While MK is great for 4 year olds, espcailly FL, don't skip the other parks. Each one has some great things for young children. (even Epcot, besides the adults need to see Epcot.)
We took some friends last trip with us. They have a son the same age as our DD (at that time almost 3) I was feeling bad we didn't get everything in I wanted to (we were there a week), but as my friend said "We had a blast each day, everyday, what more could you ask for?" So if you don't get to everything, more fun and magic to be found next trip. (oh there will be a next trip, at 4 years old they are old enought to ask to go back, again and again and again. DD isn't yet 3 and asked daily to go back, our next trip isn't until she is almost 4 years old and her new little brother or sister will be 6 months old.
Good luck, have a blast!!!!!!!