As a Floridian (45 minutes east of WDW), agree with the following from above:
Early September crowds are better. Combination of weather and kids have generally just gone back to school.
It IS hurricane season, but we don't get them often, and when we do they generally aren't strong by the time they get to us. I was actually at EPCOT the day Dorian was originally anticipated to make landfall.
Early September IS very hot and humid - I personally love this weather (that's why I live here) and think it can be easily handled if you are prepared. Light clothing, umbrella for shade, battery-operated fan. (But still make sure you wear sunscreen even with an umbrella - the sunlight bounces off the pavement and it WILL fry you like an egg.)
In my opinion, late September/October is still just as hot. Florida is just hot. It pretty much always is. Hot and high humidity. We get days of 90+ degrees in December. If weather is a concern for you or anyone in your party, I'd hold off until January/February, which tends to soften up a little on the heat (but not always - last week was in the 90s).