Taxi vs. rental car question

[Lily2012]

We are booked to sail with Big Beards for 1/2 day in the morning. We would also like to visit the botanical garden and Whim plantation in the afternoon.

Big Beards says we need to leave F'sted by 8 to 8:15 to make the tour. They gave us the name of a taxi driver to ask for.

a) Will we have enough time to rent a car in the morning if the ship docks at 8, and the Budget office opens "on island time?"

b) If we do take a taxi, would they drop us off/wait for us at our afternoon stops? How much more might that cost?

Thanks in advance for your help/suggestions!