i see you're going in 10 days......not a particularly busy time of year so i'm not sure that it makes much of a difference when you do what.....
however, as a rule of thumb, since you're staying offsite (not inside WDW) i would suggest that you avoid early opening days in the parks....that is, let's say that epcot has early opening on wednesday, then you would want to avoid epcot on that day...
early opening is only for guests staying onsite....so since you can't enjoy the benefit, why have to put up with the extra crowd of people who go there because of the early opening..
i hope i didn't confuse you with that..
so all you have to do if find out which day is early opening in which park and then just avoid that park on that day..
but really, mid september is low traffic....who would go in september?...everyone's in school.....
i sure hope the hurricanes leave you alone (this is a really bad season for florida so far)...