I'll be there that week too. I was there a week later than that last year and the crowds were non-existent. I did pretty much all of MK before 2 pm on a Friday (granted, I was travelling alone). I imagine their might be a slight increase over last year, just due to the FTP, but I don't expect anything too large. School will have just started 1-3 weeks before. Most parents aren't going to take their kids out that early in the school year.
The weather last year was hot, but not unbareable. What I mostly remember about the weather was the rain. It rained every day, usually between 5 and 7. One night there was a torential downpour that lasted all night. But you just throw on a poncho and you're fine. I do worry a little about hurricanes, but again, that's what the ponchos are for. And I'd rather be at Disney during bad weather than at work during good weather.