You can also see Belle at Enchanted Fairy tales with Belle--they do a bit of meet and greet and autographs afterwards.
Mostly, though--easy for me to say--but, try not to stress. See who you can, and enjoy your encounters. I have 4 kids and have done many WDW trips with them at various ages. I will give you some of my priceless moments with characters (I'll try to keep this brief):
First trip, older DD is 4. First day, we're in Epcot, we see Aladdin in Epcot. He says, "What's your name, Princess?" She looks at me in awe, and says, "Mom! Aladdin KNEW I was a princess!"
Next trip, older son is 3. He collects lipstick kisses like most people collect autographs. He plays "shy", and offers just enough encouragement for the princesses to try to coax him out. He's a big, fat faker, BTW.
Older DD (maybe 6?) gets half an hour, coloring with Mulan, because nobody knows she's in China.
Youngest DS (6mo) gets a lipstick kiss on top of his bald dome from Snow White, who says he reminds her of Dopey.
Older son at 4 gets picked as "Gaston" in Enchanted Fairy tales. Asks Belle to marry him, three times as instructed, and then adds, "Pleeease?". Everyone cracks up.
At a character dinner at 1900 Park Faire, all the girls want to dance with Prince Charming. Younger DS (maybe 7?) gets Cinderella to himself...and the stepsisters fight over him.
I could go on all day. My point is, you will have your own special encounters, on this trip and subsequent ones. I think we moms go nuts trying to plan out all these "perfect" scenarios in our heads, but sometimes, you just have to sit back and see how things turn out. We have many wonderful photos and videos of our kids with characters. Good thing, too--now, my "baby" is 13, and he's 6 feet tall. So, enjoy your trip, and I hope the character encounters are all that you hope for and more.