You can do both. Ask each CM if they can take any special photos. Or if you have your own ideas, go for it. Look over the photos in this thread for some great ideas. If you are going to buy the CD (only $59.95 at DLR) let the photographers know. Tell them to take as many pictures of you as they want. Some will take extra, some won't. Have fun!
The photos with Tink, balloons, stitch, mickey, minnie, etc are "magical" shots. The photographer will have you pose in a certain way so as to make the shot work. When you view your photos the added enhancements will be there. Then you can add in more enhancements. Not all photos can use all enhancements. Photos with characters can have their autographs added. There are borders you can add. Experiment and have fun with it. If you will be printing 4x6 and 5x7 make sure you save both sizes. This will make a huge difference in the photos with borders.