Consider renting points from a DVC owner for your accomodations. Check out the DVC rental boards for specific info - you can rent points from DVC owners for around $10-14 a point and stay at a deluxe resort w/full kitchen and w/d on property. A Sunday-Friday would be the most economical. A 2 bedroom would fit your whole group (sleeps 8). You can order groceries online or pick them up your self and also have the convenience of eating breakfast/lunch/snacks/beverages in your room as well as any big meals you'd want to prepare.
Park hopper passes are worth it to manage the crowds when it is busy. We often go to MK several mornings and just hop to another park when it becomes unbearable.
Plan equal park/pool time and definately take a midday nap/swim break.
Get everyone's 3 "must do" rides for each park so everyone in the group is accommodated and you have an itinerary to follow.
Definately bring a cooler bag w/snacks and drinks for your little one...it will be hot and you want to ensure you are not waiting in lines everytime she needs a drink.
Rides can be dark (bring a flashlight/light toy), loud (teach to cover ears or wear earplugs), sometimes scary (scope out the exit!). Fireworks can also be loud ---I have found it is not worth missing regular bedtime to see fireworks.
Ease into meeting gigantic characters - watch Disney movies and sing-a-longs to introduce the characters. Particularly good is a Ding-Along called
Disneyland Fun, as it shows kids singing with characters like she will see in the park.
It will be hot. Bring a water/fan sprayer from home and incorporate an "air-conditioning" strategy into your touring, so you are often sitting in cool theaters/air conditioned rides in the afternoon or eat lunch in air conditioning! Don't forget the beautiful pool -- your daughter will probably love it best!
Watch out for stroller fever -- crabbiness that sets on when a kid is in the stroller too long. Plan breaks to play at playgrounds at all of the parks and the interactive fountains as well (pack change of clothes and have her wear sandals that can get wet) so she can stretch her legs and run.
Do you ziplock pack? It is wonderful! Put individual outfits in ziplock bags and it is a snap to get ready in the am. You know clothes out of the ziplock are dirty, Dad can get her dressed in a coordinated outfit and you have all kinds of handy ziplock bags around.
Consider shipping a box of stuff to your resort including diapers, wipes, swim diapers, snacks/breakfast items, suntan lotion, spray fan thingies, etc.
Happy planning!