We took in a 12 day cruise from Miami to Miami, and explored several Caribbean islands, with two sea days on either end.
Exploring Miami
If you're new to cruising from Miami, I would recommend arriving a few days early and spending the time to take in the city. I can imagine that summer is pretty hot, but in December it was balmy. Highlights included South Beach, downtown, a harbour cruise and the visit to the Everglades. We stayed downtown, but the port is easy to get to, so any decent hotel should not be an issue.
We specifically wanted a Penthouse Suite for the space and in-room dining and don't regret the choice. Having the butler was an added benefit.