The one thing that happens right after Labor Day is they take Haunted Mansion down to get it ready for the Nightmare Before XMAS overlay that starts first weekend in October normally. Since they've expanded it to DCA the last couple of years, some of that stuff may also have some closures.
What they used to do was start all the ride rehabs right after Labor Day and doing them in cycles. Problem now is the park is overflowing in October now with all the Halloween stuff. Small World goes down in October for XMAS overlay. Then first week of November all the Halloween goes away and Christmas go up. Then 2nd week of November all the Christmas stuff starts.
So the 3 weeks in Sep is normally a lot of stuff going down. But nice thing is the kids are back in school and the crowds are pretty good & Nemo ride line should be pretty short.