Hi Carole,
September is usually a great month to visit Disney World as the summer crowds have typically left and the humidity is often not as bad. My favorite place to go when planning my Disney World vacations is
www.touringplans.com./ The site offers, for a small membership fee, access to it's crowd calendar. The calendar estimates the daily crowds at WDW on a scale of 1 to 10, with 10 being the highest levels and longest waits. The calendar is based on a number of factors like past history and special events.
I was not sure what days in September you were traveling, but I can tell you a quick glance at the crowd calendar shows that the middle to end of September is expected to see moderate to slightly less then moderate crowds. The last weekend of September is the Expedition Everest 5K at Animal Kingdom and this date shows the highest crowds because of this event. Yes you may experience slightly higher crowds at Epcot due to the Food and Wine Festival. Our experience has shown that the crowds tend to be heaviest in the evening and on the weekends as many locals visit Epcot during the weekends to take part in this fantastic special event.
We have traveled to Disney World a number of times during various parts of September and have always enjoyed the parks as well as the Food and Wine Festival with minimal crowds. A great suggestion to lower your chances of increased crowds is to visit the Epcot festival during the late morning or early afternoon when it first opens. As the evening crowds begin to increase, you will be ready to move on to another park or back to your resort.
Enjoy!