One thing to note about FP + AP, you can only have 7-days worth booked. When you use a day's FPs, you can book another day. I found out the hard way about that one. As for heat, September is about the same as July. You just have to manage. When we went in July 2015, I was expecting Hades to feel like a Winter Wonderland. It wasn't bad at all. Yes, it is hot and humid. You just need to know how and where to cool off.
Enjoy the time off and being there. With that much time, just enjoy all of it and the small things you would normally miss out on.
Just did a quick glance for full month of July rental. There is a 4BR townhouse in Regal Palms for $1,100 for the entire month.