I can't comment on October but we were there this past November 10th-17th and it was great. The crowds were very low and the weather was perfect! Our last full day was spent at MK and we rode Splash and Buzz a dozen times each. We also spent a day at Typhoon Lagoon and it was relatively emply.
The Christmas decorations were just starting to go up in the hotels.
The only thing we found crowded at all was walking around World Showcase at night because of the Food & Wine Festival.
I think this is a great time to go!
I'm sure someone else will comment on October, I know then you would have Mickey's Halloween Party.