I honestly don't know if it is required this year given that they have a limited availability to select from which means that there will be fewer people getting them. If you are committed to going you can always get one, which would be the safest way to make sure you see the show. Assuming they have the same cancellation rules, you could always cancel if you change your mind. Either way, I think they start boking tomorrow. usually that would mean 6 or 7 AM but Disney has been weird lately and sometimes they start earlier, like 6:45 eastern. I would just start checking as soon as you can.
As for the particular restaurant it really just depends upon what you want and what show they offer as part of the package. They typically do 3 a day but again, I don't know if they will do that many this year or not. Perhaps someone else may have some more info.