Hi, Amy! I would say the best place to start is exactly where you've landed - here with us Moms. You'll find that there is someone on the Disney Parks Moms Panel that will be able to answer any of the questions you have. We've all got different experiences and a variety of ways to travel, and one (or more) of us will be able to get you going.
Now that you've come to us, you will want to go to the official
Walt Disney World Resort page. There, you can set up a My Disney Experience account, which will let you keep track of all of your plans and reservations. Browse the site, check out the resorts and the ticketing options, and go all the way to the bottom to look for special offers. That will give you the basic start to your vacation.
From there, start thinking about the dining experiences you want. Do you want your little princesses to dine in the castle with the other fairytale princesses, or does your family prefer more of a "hit and run" type of dining experience, so you can get back to the attractions quicker. Are there other special experiences you think you want to include - water sports, shopping time, spa experiences, any adults only time? You can plug those in to a tentative schedule.
Just know that whatever you need help with along the way, you can always come back to your first stop - right here at the Disney Parks Moms Panel. We will do our best to help you plan the vacation of your dreams.