We have only visited in the first week of September and I would recommend it. It's still very warm,80c+ but not too humid. The parks on weekdays are very quiet and there is hardly any queing involved, but still enough people to create a good atmosphere though. If you plan your holiday to avoid the major parks on Saturday and Sunday, you'll have hardly any wait times for anything.
The parks do close around 6 - 7pm but that's not a problem as you won't have had a problem doing all the rides. Magic Kingdom stays open till 9pm each night though, as does Epcot.
I think in all the times we have visited, we have lost 3 days to rain.
What we found strange and not expected though was it stays darker in the mornings for longer and gets darker earlier at night, more so than in England.
The best advice though is as Johnny says, get to the parks early, before the majority get there, do what you want to do, go back to your hotel pool for the hottest part of the day, then revisit in the later part of the day. Once you have paid to park once, you won't have to pay again.