I went the week of Halloween in both 2012 and 2013. I will be going the weekend before Halloween this year. I attended two
MNSSHP parties each time including Halloween night. The overall crowds at all of the parks are moderate. EasyWDW, a very well respected crowd calendar/blogger, has the crowd levels as 4s and 5s out of 10 most of that week. The parties are more crowded for the parades and fireworks, especially on Main Street, but the rides are not bad. I have read elsewhere that the closer you get to Halloween the more people at the parties are concentrating on the holiday-related stuff versus the rides. There are also a ton of people who are focused on the special character meets (I waited close to 2 hours to meet Jack & Sally the first year they were there). Seven dwarfs will be long too. I got in line around 6pm. Also, from what I understand, the Nov 1 party will most likely be as crowded (possibly a sell out) as Halloween night.
The weather is much more to my liking the end of October, but is still pretty warm. The difference between 85 degrees in October with lower humidity and 90 degrees and massive humidity in mid-May make all the difference to me. The crowds felt about the same. I have read that the end of October used to be a lot slower, but has gotten more crowded due to free dining and due to the weird year-round school schedules that a lot of places have now that gives a lot of them a week off in October.
Here is a link to the crowd calendar I referenced earlier:
http://www.easywdw.com/category/calendar/10-october-2015-crowd-calendar/
I have followed his recommendations for all of my trips over the past five years and feel like he is usually spot on.
Touring Plans also has good info about the party on their blog and other info in their paid service ($12 a year). Their rankings for how busy a party will be are related ONLY to the rides. Not character meets or parades, etc.
http://blog.touringplans.com/2015/04/06/disney-world-least-crowded-halloween-party/
Last but not least, you guys should check out the "official" MNSSHP thread. It is bursting with all things MNSSHP! Don't try to read the whole 100+ page thread unless you read really fast and/or have lots of time on your hands. The same questions get asked every few days so if you just read the first page with all the info, then pickup and start reading a day or so back, you will soon be up to speed.
http://www.disboards.com/threads/official-2015-mnsshp-thread.3383728/
Sorry, so long, but I LOVE MNSSHP and can't wait for this year's trip.
And I just ate two cupcakes with frosting, so Talking Disney+Sugar=
