Rome to Pompei then Sorrento

Both your questions can be answered positively, well it is not too much, it is doable and there is luggage storage in Pompeii. You have to change trains in Naples. Take a high speed train from Rome to Naples.

Do you know how difficult it is to get from the high speed train to the commuter train that goes to Pompei? I have read that there is no elevator at the train station. I have also read that their our 2 subway services from Naples to Pompei, Should we take the one that takes reservations and accommodates luggage? If so how much time should we allow from Rome train arrival to Pompei subway departure?
Thanks

Just follow the signs saying Circumvesuviana. There are both elevators and escalators to the underground tracks in Napoli Centrale, but the old fashioned stairs are more prominent and most tourists stop searching: https://goo.gl/maps/WT5jwfSLuUB2

JR,in order to answer your second question, we need to know the month of your trip and the amount of luggage you have. Are you willing to have non-changeable train tickets? Many people on this forum have done exactly what you propose to do. It's mainly a question of crowding and comfort on the Naples-Pompeii-Sorrento leg of the trip. Because that journey is broken in Pompeii, you may not want to wait again for the special train service you mentioned, but jam onto the crowded regular Circumvesuviana (roughly half-hourly) with your third ticket of the day.

Very easily done. Roma Termini-Napoli Centrale, 1H10m. Then follow signs to the Circumvesuvian downstairs.

https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule

Campania Express. Only 4 trains a day.

https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule

In Pompeii station there's luggage storage downstairs in the tunnel under the tracks by the bathrooms. Or you walk a block or 2 to the entrance and store it there.

Guides are by the entrance, all are certified by the state and take the same test. Some are easier to understand than others. Check.

Depending on how many nights you have in Sorrento, I'd suggest going from Naples all the way to Sorrento on the Circumvesuviano. Settle in to your hotel, walk around Sorrento and enjoy the day. Then choose another day to dedicate to Pompei and/or Vesuvius, it's only 1/2 hour train ride back to Pompei Scavi station. But we had 5 nights in Sorrento, so we had plenty of time for day tripping. I found that luggage on the Circumvesuviano was a pain in the butt, so once I was on it, I just wanted to get to the hotel. Of course if you and/or your companion pack light, that makes a positive difference (my wife tends to over pack, and I end up carrying her suitcase).