I don’t have the answers to all your Qs, but I found this–
A Celebration of Harry Potter™ attendees may wear costumes in Universal’s Islands of Adventure™ and Universal Studios Florida™ theme parks January 26–January 28, 2018.
No masks, facial coverings, veils, long trains, live animals, swords or weaponry are permitted. Any home-crafted wands must be rounded on either end and must be appropriate in nature.
Costumes cannot exceed 28” (inches) wide x 80” (inches) high to meet Universal Orlando’s metal detection regulations. Costumes are subject to secondary x-ray screening. Universal Orlando™ will have sole discretion to decide whether an item is permissible.
Any item deemed inappropriate will be turned over by the owner and may be retrieved at the end of the day at the Universal CityWalk™ hub.
If a guest is spotted in a costume that is not deemed permissible, he or she will be asked to either remove the costume and change into something more appropriate, or exit the park.
Costumed guests may not give the impression that they are Universal Orlando™ Team Members.
To ensure guests’ safety, some costumes may not be permitted on certain attractions.
Bartenders and staff reserve the right to request that a guest remove any type of facial covering for identification purposes.
As guests enter or exit the parks, they may walk through CityWalk™ in costume with no masks or facial coverings, but not enter or linger in that area in their costume.