Hi Claire,
My family visited the Walt Disney World Resort last year during the last week of October and first week of November and thought that it was a great time of year to visit. The weather was still lovely and warm but definitely more bearable and less humid than the summer months and the crowds were very manageable.
One thing that I would say however is that if you will be visiting with children, I would plan to visit
Epcot on a weekday as it gets super busy at the weekends due to the
International Food & Wine Festival.
Attractions do close for refurbishment all-year round and I wouldn't say that you will be massively affected by this due to the proposed dates of your stay.
Big Thunder Mountain Railroad at the
Magic Kingdom Park is the main attraction which will be closed for refurbishment during this time.
As far as swimming goes, I am pleased to tell you that all of the outdoor pools are heated to a lovely 82 degrees all year long. My 13-year old son absolutely loves to swim each and every time that we visit the Walt Disney World Resort and I can honestly say that we have been swimming during every trip - even during the months of December and January.
Wishing you a magical holiday filled with memories which will last a lifetime!
Emma