I think they only did the Dr. Facilier dining event one year (2015). They've a parade-only viewing package at the Blue Bayou in previous years, which included the bag of candy, a light-up lanyard, and the reserved viewing for the parade. Given that, I was also kind of expecting some type of parade or WoC viewing packages this year, but perhaps they decided that the parade route is long enough that reserved viewing isn't necessary and/or there wouldn't be enough demand to justify it. In terms of WoC, that one surprises me.
As othrs have said, they've provided bags in the past. It usually features the next up-coming animated movie release. The bags are not large (they're about 9” tall, by 7” wide, by 3” deep). Children and adults are both encouraged to trick-or-treat! My group of three adults ended up with over 11 pounds of candy last year!
As others have said, you'll see a mixture of costumes, but I feel like they're more skewed towards Disney characters. Almost all of the costumes are family friendly, but there is usually at least one person wearing something that would be better suited for Universal or Knot's Berry Farm (if they allowed costumes). I think they're more noticeable because they look out-of-place.
Yes, Haunted Mansion Holiday should be up and running on the 6th. The merchandise should also be available (it'll probably be released mid-to-late August). The HalloweenTime souvies and foods should also debut on the 6th. They've said that they'll present Halloween Screams as the fireworks show during HalloweenTime, so that should also debut on the 6th.