In regards to the ADR's you can make them all once you hit 180 days.
I have not heard great reviews of GF meals at Chef's. A few positive reviews here and there, but not many. I always am extremely cautious with non Disney owned locations. As for the buffets, just like Denine said, the chef will come walk you through and poing out the GF options. They always go above and beyond for my son and offer to make him something on the back as well.