Some great restaurants on St. John - Chateaux Bordeau, Asolare, Stone Terrace to name a few. Make sure to get over to the East End and enjoy the drive, the solitude and conch fritters at Vie's Snack Shack.
A number of the car rental agencies in Cruz Bay allow you to park in their lots when in town. A 4WD is helpful if planning on exploring beyond Trunk Bay.