AS SOON AS YOU CAN, call
DVC Member services (DVCMS) to make your room reservations AND tell them that you have a Grand Gathering.
Give DVCMS all of the information about your party including names, addresses, telephone numbers and inform them of any under the age of 18.
DVCMS will then contact the GG folks and inform them of the upcoming GG.
DVCMS will get a magical gathering (MG) number back to you in a few days. It was only a day wait for me. Remember that number. It will be very important.
Call the GG people at 1-407-939-7526 to make your GG event reservations using your MG number. The Safari Celebration dinner, the International Dinner and Fireworks show, and the Good Morning Gathering can be placed on the dining plan (DP). If the DP is not available yet for when you are going, my recommendation is to call the GG people and make the reservation BEFORE the DP becomes available. If the DP IS available when you want to make the GG event ressy's, then skip this step ONLY for all ressys for which you want to use the dining plan and see below.
After the DP becomes available, and assuming that you want to use the DP, call DVCMS to add the DP and also to tell them that you will be placing one or more GG events under the DP. At that time, DVCMS will call the GG people and transfer you over to them. They will have to rebook the ressy, if you had one, under a new number and cancel the original ressy. If you had to do the previous step, then the original ressy was a placeholder until you could get the ressy with the meal plan.
If by now you are wondering if this is all a big runaround, then my answer is yes. The GG people, like the Disney dining people, do not have access to the DVC room reservation numbers, which makes all of his a necessity.