We based in Salerno for five nights in March of last year, and never regretted it. A beautiful small Italian city of 110,000, it will be much less chaotic than trying to maneuver on the Amalfi Coast. Additionally, it would be pretty tough to get anything of decent value in Sorrento at this late date.
By bus, each way it is 1 hour to Amalfi, 1+ to Ravello, and 2 hours to Positano--catch the bus where it originates right next to the Salerno train station, or on the main drag towards the A.C., Corso Garibaldi. Sorrento and Capri will be very difficult on a day trip because of time expended to get there & overall congestion that time of year. FYI there is a bus change at Amalfi to go to Positano. OR...there of course is the ferry or hydrofoil available. Not as wild & crazy as the bus ride, but certainly beautiful.
Paestum, Naples and Pompeii are all less than an hour by train from Salerno, but note that the train will let you off at Pompeii town station, a pleasant 20 minute walk to the southern Navona entrance of the ruins. Do spend at least 4 hours there, it is spectacular and not to be missed. And as Chani says, not a bad idea to bookend your Pompeii visit with a visit to The Archeological Museum in Naples another day. We didn't get to visit and wish we had.
Back in Salerno, in the Old Town there are fantastic shops, a 11th century Duomo with relics, and dare I say better food than on the A.C. A pre-dinner walk on the lungomare by the sea is wonderful, followed by a Margherita pizza at Pizzeria Trianon, the best pie I've had in Italy to date, for a cost of all of 6 Euro. The original Trianon started in Naples in 1929. You have made a wise choice.
Enjoy your trip!