I think your pref dress is fine! It's usually a good idea to wear something non-black so as to stand out from the sisters, who usually all wear the same color, often black.
If you receive a bid, the first thing you'll get from your new sorority is a lot of gifts, including a t-shirt. You'll probably get the chance to change into it, then there will be lots of pictures taken.
Hopefully one of the ladies from UF will be able to help you with your other questions.
Good luck!