Day trip from Sorrento to Amalfi suggestions

The SITA bus kind of runs on schedule. You won't be the only folks at that bus stop thinking you'll beat the crowds. Usually the bus is jam- packed and SRO. Often it doesn't stop for passengers because there's no room to board more folks. Last May, we saw lines of folks almost blocking streets waiting extended time for those buses. This is not the makings of a great day.
Both Positano and Amalfi will be should-shoulder crowded. I did not find that pleasant.
The ferry can be canceled if rough water or a storm comes in. Never plan on taking the last ferry of the day back.
I think you'd be better with a shared Mondo van tour, or a shared boat tour. The scenery is really better from the water.
Note that a driving/van tour is about 9 hours, of which you'll be in the vehicle for half that time.
The infrastructure has been sadly neglected in this area . It's a victim of its Instagram success.
The area is beautiful, but be prepared for the realities on the ground, and your trip will be much more enjoyable.
Safe travels!

Pat beat me to it, when we walked by the bus stop at 8am in April 2022 in Sorrento the line was down the street. You may be waiting for the next bus, or the one after that. The lines in Positano can be worse. It's just a local transit bus and you can't reserve a spot. For me, Positano was worthy of a quick look and then move on. Amalfi was more interesting and Ravello was the best of the bunch. We used Mondo Tours and don't regret it even though as mentioned above, of a 9 hour tour, 4.5 were in a vehicle. We spent an hour in Positano which was more than enough, 2.5 hrs in Amalfi which was good and then an hour in Ravello which wasn't nearly long enough.

I enjoyed Capri significantly more, the views were just as spectacular and it was faster and easier to get to giving you more of your day to explore.

You have some good ideas here. Do not discount their warnings about your peak-season trip. A group tour is more "sustainable", but we hired a car and driver through our Sorrento hotel desk. Positano was also a must for me, but mostly a disappointment. You can walk by the same international branded boutique shops in any European capital, alas. I hope Ravello does not become like Positano.

We need a post-renovation report on 2024 ferries in Positano. Can the new dock take larger ferries? What happens in boarding the last two ferries of the day? Do they check pre-bought tickets?

Is the ferry system an actual magical relief from bus crowding, or is it already over capacity like everything else?