Speaking from experience, in Cuba I'd keep it casual and easy to wear! Lightweight cropped pants or shorts, tees, and crossover athleisure type stuff really work well. A casual jersey or tee-shirt dress or two, or a skirt in an easy non-wrinkle fabric will take you through a day of walking around and to dinner in the evening easily. A couple pairs of comfortable shoes that will take you over cobblestones and all kinds of roads and terrain.
I recommend a hat with a floppy brim so that when you turn your camera sideways for vertical shots, the camera is not bumping your hat back on your head.
Check out the Lowepro Slingshot for a good sling type camera bag. I also got a Mind Shift rotation type bag which I'm really liking. Their bags are really nice -- they're a division of Think Tank, so I trust them.
I'm so excited for you! Have a wonderful time! You will enjoy it. Don't miss dinner at La Guarida, and take your camera when you go there -- the building is way cool.