Here's what I know about Crocs:
1. To second other posters' suggestions, definitely try them on in-store to get your correct sizes. For example, I wear a 7.5 shoe (womens) regularly, but I wear an 8 in Cayman and Mary Jane, and a medium (8-9) in Beach.
2. Disney Crocs are Beach Crocs for adults; Disney Crocs are Caymans for kids.
3. I wear Crocs with socks. I wear socks with my Crocs. I try to avoid stepping on rocks when I wear socks with my Crocs. (OK, I channeled Dr. Seuss there, for a minute

). But in all honesty, I try to find ankle socks that closely match my Crocs, rather than wear garrish white socks with my Crocs. Someone else on the DIS recommended this to me, and I highly endorse that recommendation!
4. Try on in-store, order online! If you are new to Google checkout (simple type "checkout" into Google) you can get $10 off your first purchase. If you catch a Dick's sale, you can get $29.99 Crocs for a low as $13.99! That's how I got my Mary Jane's. My motto...never pay full price!
5. Jibbitz are cool, but they do not work in Disney Crocs without modifications (search the boards for crafty recommendations). But I wonder...why buy Disney Crocs with the adorable Mickey Mouse head holes if you're just going to fill them with Jibbitz?!? Put Jibbitz in regular Crocs and enjoy the Disney ones for their Mickey head holes.