Matt, unless things have changed it looks like your trip is going to be "...in February or early March, when it’s not so darn busy."? I picked that up from one of your previous threads:
And don't confuse # of nights with # of days, OK? If coming from Florence, it'll take you some time to get down to the coast so 4 NIGHTS in that region translates to less than 3.5 days, and daylight will be rather short. That's still enough time but, well, you get the idea? Also, the smaller the location on the coast - Positano versus Sorrento or Salerno, for instance - the more time-consuming it can be to get there and to get around from, depending on where you want to go. The larger bases will also provide you more open tourist amenities, such as restaurants, in winter + ferry service to Capri. Ferries do not operate from Positano or Amalfi during the winter months.
As we previously discussed, weather could be a crapshoot that time of year so another plus for Sorrento (or Salerno) would be the ability to jump a train into Naples on a wet day to do some indoor sightseeing; there's little of that to be had on the coast.
I would choose Sorrento over Salerno if you want to do Capri: ferries take 2 hours from Salerno and there are few to choose from, if they even run to the island during winter.
Capri? I'll probably be the minority here but as you are hikers, I'd stay a night or two on the island. We really enjoyed our treks to various points, and it was a great way to lose the day-tripping crowds clogging the main parts of the two little towns (Capri and Anacapri), although the mob will probably be much lighter in winter. The island takes on a different ambiance at night when all those day-trippers go away. :O) Granted, many shops and restaurants will be closed but hoofing around the island can be done any time of year (assuming weather permits), the chairlift to Mt Solaro will be operating (you could hike down from the mountain if desired),
Hiking ideas (and you do NOT need a tour):
You do NOT want to be in Capri on the night before a flight out of Naples or Rome. I wouldn't even want to be in Sorrento if that flight is in the morning.