8 is all you need for group dining and I think it may be 10 for the select gathering stuff- call the magical gatherings tele line to ask… there were not many “perks” and many “put outs” when we did it with our party of 18 the last time. We were stuck at seperate tables,put in corners and in back rooms for character meals and given odd times for reservations to accomodate our party size and when it came to paying for our dining it was a nightmare. Im only saying this all because we had so much trouble that my husband is insisting on it being just us this trip. I spent alot of the last one in tears from all the troubles. Anything that is an actual Grand Gathering event is a seperate cost-
Personally I would just plan it out as if you were seperate parties and then meet up when you wanted to. Its a lot less stress!