We have gone twice in September. Free dining usually offered late August through September. DEFINITELY hot enough for the water parks. LOL. Crowds about as low as it gets. This is when we are going this year. Aug 30-Sept 8.
Last year, we went 2nd week in November. Too cool for water parks. We thought the weather was truly lovely, though. Free dining only available for part of the month. The 14th was the earliest free dining day last year. Definitely busier than September, but really not too bad. Christmas decorations were beautiful, too.
What you're looking for--low crowds, free dining, water park weather--would be best found late August.