is there a walk-on shuttle bus from mia to miami beach? or do we need to book in advance? we are thinking that if we book in advance and then take hours to clear immigration we will miss the bus. or will the ticket be valid for any bus? what is the likely time it will take to clear immigration? we are staying at the winter haven hotel for 3 nights then renting a car to tour keys,etc. are there car hire companies close to this hotel? does the shuttle bus stop at various places, or go to just one place? thanks.