Julie,
Disney has not announced availability dates for Belle's Castle, so it is hard to say. I would not count on it, and if it surprises us and is, then you are all the luckier!
As for the favorites of the choices listed, for the average "Princess-in-Training" either
Cinderella's Royal Table or
Restaurant Akershus are the best. I love
1900 Park Fare, but for that first time the others offer more princesses, which means more "A-List" celebrity sightings.
If I had to choose between the two, I would say our girls prefer Cinderella's Royal Table, because of the venue, but we prefer Akershus for the food.
I recommend starting with Cinderella's Royal Table, with breakfast, then dinner, then lunch as the preferred order of preference. That is because breakfast really sets the mood for the day. If you are going to Akershus, I would lead with dinner, then lunch, then breakfast, because that half of the park has better ambiance at those times. Regardless of which of the 3 restaurants you get, you will love the experience!
I hope that this helps? Write me back from my bio page if you have any follow-up questions!
Have a magical (and delicious) vacation!