We're going then. From what I can see, the grad nights effect you if you want to do MK in the evening on a Friday or Saturday night. We usually do MK early and teenagers don't like to get up early, so I feel ok with the grad night on Saturday....we'll hop to Epcot in the evening.
I think the flower show goes on for many weeks, but am not sure. Since Epcot handles crowds so well, I can't imagine that will be too terrible either. I was in Epcot last year during the Food and Wine Festival, and it wasn't bad...a few more drunks than normal, but that's all.