You should have a great trip in October. I know you said you are not going on a weekend, so that's probably good, but you'll also miss our Fantasmic! which most (but not all) agree is superior to the DHS version.
Be aware that with last month's splurge on Halloween, the event quickly became extremely popular as the word quickly spread amongst locals and Passholders. I have no doubt it will be even more popular this year. It essentially means there is no downtime in October before November and the Holiday season stuff starts.
This year they are spending even more on decorations at both Parks. Mansion goes down on Sept 4 for the Haunted Mansion Holiday overlay and will re-open on Sept 21, which is the same date all the other HalloweenTime decorations will make their debut.
FYI, Storybook and Casey Jr go down for 2 months on Sep 4 also. Not a huge deal or anything, but your kids would probably have enjoyed them and they're not something WDW has obviously.