How big is the museum and are there a lot of exhibits?

2 buildings yes it's enough to keep u occupied for atleast 4hrs.there is even a mini viewing room to watch different movies on miami history with movie seats

The place is not actually too big. If you are not interested in some topics, you could manage the museum in two hours. For me the second building with recent history was not too interesting.

Great place to experience Miami, from the Pirate days to Cuban & Haitian immigration to present.