Check out the Restaurant board!! I believe there is a thread about eating at the Royal Table.
In general, this is the most difficult meal to get ADRs for..especially at breakfast. If you can be flexible and do another meal, you may have more luck.
As for the differences, I believe that breakfast and lunch are basically the same with the princess interaction. Cinderella is in the lobby and other princesses circulate during the meal. The dinner meal is not a princess meal.
One big thing in your favor is that, beginning Feb. 1, there was a significant price increase for all meals. You now get pics included. It also went from a regular TS to a signature meal, meaning that it took 2 credits to use it for the dining plan. Many people have decided it is no longer worth it because of the recent changes. I've been advised that I should not anticipate a problem getting ressies. Of course, I'm planning much further out than you are.
It certainly can't hurt to call. If you haven't done so already, please don't tell your dd until after you do get reservations. There is also a princess meal in Norway (Epcot), and a Cinderella meal at 1900 Park Fare (GF).
Good luck....and have a magical trip!!!
