Well hello again Aurora! I'm so excited to be able to talk about one of my favorite events. I actually just answered a question that covers the first parts of your question, so I'm going to
link you there, mostly so I can have more room to answer the rest of your questions! ;) To recap, costumes are not mandatory but I think they add to the fun of the evening's events. It's super fun to have cast members, guests and even characters commenting on your costume.
As far as restrictions, the official rule is adults are not allowed to dress exactly like Disney characters, so as not to confuse other guests. If you
do decide to get your Tinker Bell or Cinderella on during the party, you're asked not to pose for pictures or sign autographs. Children are free to dress as Disney characters.
In addition, nothing inappropriate or too scary/gory is allowed. Full face masks and large or dangerous props are also a no-no. For example, if you went as Glenda the Good Witch and had a magic wand, that would be fine, but going as the Wicked Witch of the West with a full-sized broom might be a bit of an issue. I'd say a general rule of thumb is any props that look like weapons would probably not be allowed in.
The party begins at 7pm and lasts until midnight, but you can pick up your wristbands with your ticket any time after 4pm at various locations within the park and at the gate.
Each guest is provided with their own trick-or-treat bag from Disney at the Magic Kingdom entrance. However, I have seen guests bring their own bags and you certainly are allowed to do so.
I hope I've answered all your questions, but feel free to ask another if I left something out or you'd like more details. ~Suzannah