You'll need a car the island is a good size and the best beaches are a little drive. We own at the Sea Aquarium and like it, theirs a new grocery store close by that has every thing you'll need and you can use the shuttle or follow in your car.
Most of the beaches have food look on shorediving.com for maps as the best dives are from the very beaches, some have dive operations on site. Maps can be printed out before and good discriptions are give on this site about ammenites and such even for non diver.
Must do beaches are Cas Adou and Porto Mari both have great snorkelling and diving. Jan Theil has a good restraunt and is good day or night. You won't have a problemn finding things to do, try the slave museam in town and the flowting market.
Have fun