We just got back last week from our October vacation (10/25-11/1). The weather was still warm (high 70's to low 80's during the day and mid 60's at night). DH was there from 10/21-10/25 for a conference and the temps were in the 90's.
When we were at MK on 10/29 it got cooler at night and I actually had to switch from my shorts into jeans. But other than that, it was fine. We had rain one day (on 10/28) but it was over before we even left for breakfast at around 7, 7:30 am. That was the only morning where the temperature was 58 degrees (but it warmed up during the day and was fine).
We went to
MNSSHP on Halloween night around 7:30, 8 pm, and the parade was just about ready to start. A few of the CM's told us to wait until 10:30 as it's not as crowded as the earlier one. We opted to do that and spent about an hour going on some of the rides and hitting the candy stations in tomorrowland before heading over to Toon Town. The major rides are open during MNSSHP and we didn't wait too long on the rides that we did do. Those that are closed are used as candy stations.
Our DS4 got his face painted like Goofy in Toon Town, but within 5 to 10 minutes, he was out like a light! We couldn't even wake him up for the parade! Daddy wound up going ahead and Trick-or-Treating for our DS
Overall, you should be fine. Just make sure to bring a sweatshirt or a light jacket with you to the parks for the evening/night.