Ah thematic portfolios...I'm in the same spot in my photo (well actually art) class. But I'm not doing mine around Disney, even though that would be awesome! I had major issues coming up with my theme so I did a word association and also a free write on the topic. But since you have to do it based around a quote here's what I came up with....
"I only hope that we don't lose sight of one thing - that it was all started by a mouse. " - Walt Disney
You have a Mickey in every photo, whether it be a prominent or in the background/not the focus or hidden or obvious.
"I try to build a full personality for each of our cartoon characters - to make them personalities" - Walt Disney
I don't know if you are going down with anyone else but you could do photos of them interacting with the characters. Candid shots to show the personality of the characters and how they make the guests feel.
Just google Disney Quotes or quotes about any topic you associate with Disney and I'm sure you'll be able to come up with something. PM if you want any help. I'm all in the mindset of thematic portfolios thanks to my class. =)