We went Columbus Day weekend 2001, I know that it was right after Sept. 11, so the crwods were probably lower than usual.
The only bad day was the Saturday of Columbus Day weekend.
Magic Kingdom was packed.
Since they only have fireworks and Spectromagic on Saturdays during October EVERYBODY was there to see it.
Luckily, they annouced that they added an extra parade due to crowds, so we got to stay at MK longer and enjoyed the 10pm parade which was less crowded.
As far as hours, from my recollection MK usually closes at 6-7pm week nights and 9pm weekends, MGM 7:30pm, AK 5:00pm, and Epcot closed after the 9pm Illumintations.
The two times we have been in Ocotber, the weather was great, mid 80s not too hot but still good for swimming. In the evening there sometimes was a slight chill but it didnt keep us from swimming.