Hi T,
Our trip this October will be our third at this time of year and it's definitely our favourite for crowds and weather. Maybe we have been lucky, but the only rain we've experienced at this time of year was on our very first trip and our very first visit to a WDW park (MK) on our first day. It rained for about 20 minutes as we entered the park.
Again, we've been lucky with the temperatures - what I would describe as sublime summer days in the UK. We went the last two weeks in August/first week in September in 2000 and had lots of rain/thunderstorms, and it was <i>very</i> hot.
We've done Halloween Horror Nights at Universal which is a scream (excuse the pun!) and we'll be doing it again this trip, although the venue is moving to Islands of Adventure for the first time this year. Don't miss the Bill and Ted show - excellent!
Mickey's Not So Scary Halloween Party at MK will be a first for us, although we have done Mickey's Very Merry Christmas Party and I'm expecting it to be similar.
Our favourite event of all is the International Food and Wine Festival at Epcot's World Showcase. We spend the entire day wandering from country to country sampling the food and drink offerings (ranging from about $2 to $5 for the food).
The parks do close earlier - about 6 or 7pm for MK (unless Spectromagic is scheduled when it's about 9pm, or
MNSSHP which is a separately ticketed event), normal time for Epcot (9pm), about 7.30pm for MGM, 5pm for AK, various times between 5.30pm and 7pm for Universal, 7-8pm for IoA (except for HHN nights - separately ticketed event).
We've never noticed huge crowds during October. We have always avoided Early Entry days which have now been suspended, so it will be interesting to see how this affects crowd patterns.
It's always been warm enough for us to swim during the evenings - like I said we've always experienced high temperatures and good weather. We do pay to have the pool heated, though, even in the summer months. I wouldn't say it's necessary, just preferable.