We have been the first week several times. The crowds did not bother me as much as the heat. I live on the Gulf Coast in MS, so I know heat and humidity. The most it bothered me was in Epcot because there is very little shade. It is a good time to go though as long as you take breaks in the day, hydrate and avoid Epcot on weekends due to F&G. For some reason the Butterfly House reminds me of crowds. It is just too small I think for the F&G crowd.
Our trip is 5/1-5/8 so I will be there too with DH and my Mom and Dad (their first trip to F&G)