Note: Pompei is the name of the new town which is on the
Salerno-Naples train line while Pompeii is the name of the ancient
ruins which are on the Circumvesuviana train line. The two train lines
are only a couple of kilometers apart at that point.
Thanks, Frank--never knew that! On the train line and also the Circumvesuviana line, it's 'Pompei', and I had thought it was the Italian spelling and I was using it exclusively.
First off, LSD, kudos to staying in Salerno. I have stayed there for 5 nights and recently Chani did as well. Great base as you'll find out, very chill and in my opinion the 'real Italy'. Try Pizzeria Trianon for true Napolitan pizza. It's a dive but cheap & great.
We did Pompeii from Salerno in March 2015. Took the Trenitalia route to the Pompei-town stop in about 50 minutes, and there was no taxi to be found, but it was a nice day so we walked the approximate half-mile to the southern entrance. That time of year, did not see any touts asking to be a guide, but if there are, and the cost is not prohibitive--no more than 20 Euro--why not I say? The brochure they give you upon admission is pretty much worthless, and nothing is marked. You can also hire a private guide in advance, at quite a bit more money. Either way, plan on spending a good 4 hours there, and you will have still only seen maybe 70% of the ruins.
Speaking of, if you are really into the archeological aspect, I don't see Naples on your itinerary but all the art from Pompeii is at the Archeological Museum there, has been since the mid-1700's. It's a 50 minute train ride from Salerno, then a 15 minute taxi ride. Well worth it if you get the chance.
Finally, I would combine Ravello/Amalfi/Positano in one day, and for this one I would recommend the SITA bus from Salerno station (55 min), only because it's a real 'trip'. Hopefully it won't be too crowded that time of year--sit on the driver's side and hang on--the cliff dropoffs out the bus window are something else, and it's really cheap entertainment! You will have to change buses at Amalfi for the 45 minute continuation to Positano. Then maybe take the ferry back to Salerno for a nap, then a nice dinner after 8:00, because that's when the Salerno restaurants start serving dinner--that's a great day of touring!
Enjoy your planning!