The desserts on the buffet are included in the price of the buffet. Of course, they are also "all you can eat"...If we were sans children, I'd probably start the buffet at the dessert table!
We have never done breakfast at Chef Mickey's, but one of these days....
It has become a tradition in our family to start our trip with dinner at Chef Mickey's. We eat here on our first night. After dinner, we shop a bit at the Contemporary (kids always want to spend a Disney dollar or 10!) and then we hop the monorail and do the loop. Last trip, we had UPH, so we went into the MK to watch Wishes. It was a great first night!!!