Pompeii Ruins from Pompeii train station (not Pompei Scavi Villa Dei Misteri train station)

Have you considered a taxi? I would discourage much walking to save your strength for Pompeii itself. Good luck and have a great trip. Pompeii is fantastic. Safe travels!

Piazza Anfiteatro is a one-half mile walk from the Pompei Train Station— so about ten minutes.
Piazza Esedra is one mile from the Pompei train station
which is just about the same distance as The Pompeii Scavi- Villa dei Misteri entrance.

If you care to, you can study this in more detail using Google Maps, which will also compute walking distances for you. There are certainly plenty of people staying in Salerno, but only a few of them post here. So we have to hope some more details appear in other replies.

We did this exact trip in Jan 22.

We stayed un Salerno, we caught the train from Salerno (From the Duomo stop as our place was only 200 metres from this stop)

Its on the Trenitallia line and stops at Pompeii Station.

From there, its an easy 15 -20 min flat work to the first entrance, which I assume was Piazza Anfiteatro. The second entrance is up the hill and is about another 10 minutes

At the first entrance there were heaps of stalls. We didnt look out for guides, as we had booked a tour guide with Pompeii and Herculean together (which was fantastic)

We did it early morning in Jan, and was easy, in the heat may be harder, but we would do it again.

We were two 45+ people and two kids 10 and 13.

if you are in Salerno, you should also consider Pasteum. We loved Pasteum and it was quiet

Trent, That you for the great information. We are planning to do Pompeii and Herculaneum in the same day. Would love to know what tour guide you hired if you don't mind sharing.

Sorry for the late reply

We used ASKO tours. It was a group tour with about 20 people in it. It was a tour with an archeologist and we learnt a lot

Started at Pompeii and we had about 3 hours in Pompeii. Then caught the commuter train to Herculaneum. Had over 2 hours at Herculaneum. This is enough as this site

We then walked about 20 min downhill to the trenitallia station on the harbour and caught it back to Salerno.

We chose this as we had kids and didn’t want to spend too long at each site. As adults we do want to revisit Pompeii.

The guide was great navigating us away from people in Pompeii. However we were in Jan so was quiet compared to summer.

We would 100% do this tour again

Reach out if you need more info.

https://community.ricksteves.com/travel-forum/italy/train-from-naples-to-pompei-and-then-to-salerno

In March, 2015, we took the train from Salerno to the Pompei station, deciding to walk to the nearest entrance which was Porta Marina. That was approximately a .75 mile walk and on a nice day, temps in the 60's, it was very pleasant walking through Pompei-town, which was very cute but with the requisite souvenir shops. At least at that time, by the city hall there was a monument to 9/11 with a bronzed girder from the Twin Towers. Very moving.

So, we entered the ruins--do not remember seeing any guides hawking their talents--and spent about 4 hours walking around, seeing maybe 50% of what was there, and getting very tired. We had brought a couple panini & waters in our backpack, sitting by that amphitheatre not far from Porta Marina and having lunch, which I guess is somewhat of a no-no but we totally cleaned up after ourselves. That was really neat.

Soon enough, we were getting really tired--cobblestone-walking is exhausting!--and knew we would not be walking all the way back to Pompei station. So we exited by the Scavi entrance, flagged down a taxi that took us back to the Pompei station for our ride back to Salerno. Think it cost 15 Euro for a 5 to 8 minute ride, well worth it to us. The dogs were tired!

If we do Pompei next April, we'll probably take the train into Naples, walk downstairs to the Circumvesuviana train that will take us to the Pompei Scavi entrance, and then backtrack when we're finished, possibly stopping in Naples for pizza. At that entrance, I know there are tons of guides wanting you to hire them. Back in 2015, I seem to remember the going rate being around 20-30 Euro.