Day Trips to Amalfi, Positano, Capri out of Salerno

Yes, all are accessible but you have more transport options (ferry versus bus) if traveling during high and shoulder seasons as ferries do not run all year.

Ferry schedules: use the dropdown for schedules between specific points. You will, of course, be limited to ferries for Capri, and some point-to-points, like Salerno>Capri, will be time consuming:

http://www.naplesbayferry.com/en/schedule?from=salerno&to=amalfi

You also have the option on]f SITA buses for the coast. Again, use the dropdowns for schedules from one location to another:

http://www.positano.com/en/bus-schedule?bus_route=salerno_maiori_amalfi

The Amalfi Coast towns are all easily accessible on the SITA bus from Salerno. There are two lines, one goes from Salerno to Amalfi town, the other from Amalfi town to Sorrento. For Positano, you'd change buses in Amalfi. Ravello is perched on the cliffs above Amalfi and there is separate bus service from Amalfi there and back, though some prefer to walk down and enjoy the views.There is also ferry service along the coast from Salerno. Some of the other towns are not served by the ferries, only by bus. It's farther to Capri, and you'll probably need to change ferries somewhere. You can also visit Paestum (ancient Greek temples, archaeology museum) by bus or train from Salerno.

Pat, it's crucial to know the month of the year for this planning. As noted, most of the transport has seasonally adjusted schedules. And the Amalfi Coast is incredibly crowded in season. The fact that you're sleeping in a less-visited city doesn't help the massive traffic jams on the two-lane road that serves most of the A.C. towns. Even if you hire a private car and driver, the car still has to negotiate that road. You also have to deal with crowding on ferries. For a high traffic place like Capri, I would buy my return ticket with my outward bound ticket, so as to be certain of getting back at the end of the day. We found that our return ferry used a different pier number than the one we had arrived at, so look around the port and try to find where your boat is going to be.

I note that you didn't mention Pompeii. Presumably you have researched how to get to the ancient city's excavation from the modern city of Pompeii, which is where the train from Salerno stops. (People sleeping in Sorrento take a different train line, that goes directly to an entrance to the ancient site.) I happen to be sorry that we didn't have time to see Paestum from Sorrento; it was just too far for a daytrip. But not everyone goes there - see if you need both Paestum and Pompeii. (They are certainly not interchangeable attractions.)