Hello, Christina!
What an exciting trip you are planning for your own little princess!
For starters, I'd go to the main
Walt Disney World page and enter the dates you'd like to stay as well as the number of people in your party. Because you already know that you'd like park tickets included with your hotel, then select "packages" on that page. Where the site asks you to specify a resort hotel, leave it on "no preference." This will give you a better understanding of the variety of accomodations available to you, as well as the cost differences among the various categories. That's a great overview of options from the start.
Regarding meeting the princesses, you'll find them throughout the four major parks. However, if you'd like an even more magical experience, there are several dining locations at which your own little princess can meet a princess or several princesses, one after the other!
Look through your choices on Walt Disney World's Character Dining page for more details.
One last suggestion: consider the Disney Dining Plan if you plan to eat in the parks. This will help ensure that you all take a break each day, relax, enjoy some wonderful food and each other's company. It will even save you money!
Please send me all of the additional questions you're bound to have as you plan this most exciting event! I really love to help!