Hello, Latha,
When you arrive at the parks, you'll want to get a copy of the
Times Guide, which is located with the park maps. This guide will list all of the characters that will be greeting guests as well as the times/locations. So, you won't need an appointment, but you will likely have to wait in line. Cast members will be there to assist you with any questions and will even take pictures with your camera if you'd like a photo of the entire family. You can also stop by Guest Relations at any of the parks to have them check where Belle will be during your trip by having a cast member call the Character Hotline.
The characters do a wonderful job interacting with guests; and the princesses often have short conversations, too. You are welcome to bring an autograph book and a pen (fat pens work well for many characters with costumed hands).
And if you haven't heard, there has been a renovation going on at the Magic Kingdom.
Fantasyland has been adding some new attractions, including
Be Our Guest Restaurant and
Enchanted Tales with Belle. Also, Belle may be found at the French Pavillion in the World Showcase at Epcot (look for not-so-hidden references to her story in the shops).
Have a wonderful trip and please let us know if you have any further questions.