Avoid EMH days.....even when I stay on disney property and go to EMH, I'm out of that park by 11 or 12 noon.
As far as going in lower crowd times. As far as I'm concerned, that is more and more becoming a thing of the past. Sept is generally quiet after Labor Day but last year they had
free dining on wdw property and it got quite crowded. Early Oct used to be generally slow, but we were there the first week of Oct 2006 and it was quite crowded. Sat, Oct 7 was PACKED solid in Epcot (which to us, usually feels like the best place to be to handle crowds because it's so spread out and has wide walk ways). But
MNSSHP got earlier and earlier.....and Food & Wine also goes on earlier than it used to many years ago. The first week of Nov used to be generally quiet.....not anymore. There's Food and Wine, Jersey Week, ABC Super Soap Weekend, and this year there is a
DCL pirate pin trading event mid-November.
We were also in WDW the first week of Dec this year. Again....used to be quiet....all wdw resorts were sold out for the first weekend.
Our plan of strategy is get to the park bright and early. Be in the parking lot by 8:15 am. Avoid an EMH (morning or evening EMH) park of course. Fast Pass all you can and get out by noon. Return late, by dinner time, and plan to wait. Fast pass when you can. If you are at a park where it is the only one open late for the night...think long and hard about whether you want to be there. The MK was open until 11 pm on Feb 24. Epcot closed at 9 pm and MGM and AK were closed even earlier. The entire guest population (on and offsite) flocked to the MK that night. It was a nightmare. Why wdw can't keep at least 2 parks open late during a busy season (it was Pres Week), is beyond me ! We got there and left within about 90 min and headed out to see a movie. Also, some nights during the week the MK may have Spectro. It may be only a night or two during the week---count on the MK being packed to the gills those nights.
In the past 6-7 months, we've been to WDW in early Aug '06, early Oct '06, early Dec '06 and mid-late Feb '07. Each trip we encountered very large crowds most days. There were exceptions here and there, but they were a rare treat.
Since you will not have "hoppers", I think you really need to be prepared for whatever comes your way. Hopping is one of the best perks one can invest in (that and the Fast Passes) in order to survive the crowds. Best of luck to you.