Best Way to Book Excursions & Private Drivers? (Sandals Grande, St. Lucia)

Hello! For our honeymoon, we're staying at Sandals Grande in St. Lucia.

1. We're hoping to do a couple excursions (i.e. speed boat tour, catamaran sunset cruise). Is it typical to just book these when you arrive at the resort? Or should we book ahead of time to ensure we get a spot locked in? We'll only be at Sandals for a few days...

2. Any recommendation for private drivers/driving companies? We need to get to another resort (Stonefield) halfway through our honeymoon.

Many thanks!! :)