Cruise question: How convenient is it from the following ports to attractions?

For most of the places you mentioned, ships either stop in town, or very near town, and it's all quite convenient. My caution is for Katakolo. The town itself is ok for an hour's walk through tourist shops, or for a meal in a restaurant by the water. But the only reason ships stop here is to bring people to ancient Olympia. Olympia is a 25 minute drive. Unfortunately, because Katakolo is so small, and because the locals know where you want to go, the taxi and car rental prices are exorbitant. (Astonishingly exorbitant). Your best options are to go with the ship's tour or to take the train. The bus is also an option, but there's a chance you'll have to switch buses in Pyrgos halfway to Olympia.