If you think it's a far drive from Miami, you should try driving there in an old RV from southern CA! We did that in 1987 and it took almost a week to get there! If you are driving, 7 mile bridge is not to be missed! (Actually, if you are driving down, it's not possible to miss it! LOL)
On Key West, I have good memories of the giant shell shop. When I think about it know, it reminds me of Spongebob.
More recently in 2001, Key West was our last port on a western Caribbean cruise. We went in early Nov and the weather was great!