Ins and Outs of renting a car on St Martin

Hi:

My wife and I will be staying at Le Meridien L'Habitation in March.
Many suggest renting a car due to the relative remoteness of the
resort.

Do I rent once I get there? Should I arrange ahead of time through a
travel agent? What if I won't need the car for the whole time? Will
availability be an issue? Do you buy insurance or is it figured into
the cost?

Thanks!

Jon