I went on a vacation from the 22 to the 27th. Enough time had passed from the late august, early september occurances (SWGE opening, Dorian scare, etc) that it was more of what a typical september was like.
I'd Only been before on spring break in march/april and the heat was similar, but at least, I personally felt it less humid, if Only a bit. Still Hot, but nothing too extreme or unmanageable, and we also had not a single drop of rain that week.
Crowds were the worst at the Halloween party, and that was mostly for walking purpose, wait times were mostly fine. Regular days at the Parks were 15-20 minute waits in average, but the big attractions never went above 50 minutes. The most we waited was 25 mins for SDD over at Hollywood Studios at about 7:30 pm. Stuff like Dumbo, It's a small World, The three caballeros, said 5-10 mins but were walk-ons.
We took Minnie Vans to and from the Parks, and I think those were the longest wait periods we had, specially at night, about 15 minutes or so, which isn't really a bother.
Overall,it was a great trip, and September became our default month for our y early visit from now on.