Hey there Adriana,
Welcome to planDisney and thanks so much for your question! I'm happy to hear that you will get to spend
Star Wars day at the Happiest Place on Earth - how fun!
As part of the
Star Wars Nite special event, the event page does encourage Guests to dress up as their favorite
Star Wars character, but just keep in mind the resort
costume rules. Specifically, I would note the policy that says "Clothing that drags on the ground is prohibited in theme parks." Since it sounds like you'll be wearing a cloak/robe, I would then just make sure it does not drag on the ground.
While it does sound like you should be alright - especially since you can purchase Jedi robes in
Black Spire Outfitters - it will ultimately be up to the discretion of the Cast Members, so make sure to follow their guidance when you arrive.
The party begins at 9:00 PM but your special event ticket also gives you access to Disneyland Park as early as 6:00 PM. There will be exclusive themed food, beverage, and merchandise options, music and shows like the Lightsaber Instructional, and - my favorite - character meet and greets! It's sure to be an out of this world experience.
Thanks again for your question, Adriana! I hope you have a wonderful time celebrating in a galaxy far, far away.
Have a Magical Day,
Greg