In 2016, we visited Disney twice. Once was a short 3 day trip starting on Memorial Day. the other was a 13 day trip starting October 1st through the 13th. The crowds were much larger Memorial Day week. While October has grown in popularity, and is busier than it used to be, some of the doomsday stuff you read on here is overblown. There was some weird stuff going on last year. The hurricane messed with a lot of schedules and made getting a meal at a food court at the resort virtually impossible. And, then the last few showings of the Electrical Parade occurred while we were there, so that brought in a lot of locals.
Is MK crowded on nights it's open late? Absolutely, because so many days it closes early because of the Halloween party. But, if you go there in the morning of a party date, then it's very manageable. With careful planning, utilizing rope drop and late nights, park-hopping, and a sound FP+ strategy, we were able to have virtual walk-ons on every attraction except Test Track (we chose Soarin and FEA as our Tier ones on our two primary Epcot days).