I have stayed in Sorrento and done just what you suggest multiple times, always enjoyed it. I have taken the bus from Sorrento to Positano, then on to Amalfi and then the local (tourist) bus up to Ravello. I have also taken the ferry from Sorrento (stops in both Positano and Amalfi). I've also done trips where I did the bus one way and the ferry the other.
The ferry is seasonal and not that frequent (I think two each way per day) so you do have to be aware of the times. The bus can get very crowded and some people suffer from motion sickness on it but the views from both the bus and the boat are fantastic (and different) so if you have time it's good to do both. Best bet for the bus from Sorrento is to get to the bus stop at least a half hour before the first bus.
Positano is very vertical. But it's also quite small and if you don't want to do a lot of shopping in expensive tourist clothing shops or eat a sit down meal you can see it in a short time. It's gorgeous though, especially from the water and also from the upper road (where the bus runs) looking across the town. I enjoy Amalfi more, for exploring and walking around. Also love the walk from Amalfi to neighboring Atrani. We took the bus up to Ravello and then walked down. Hard on the knees but at least it's down hill.
Easy to do day trips to Pompeii and Herculaneum (and Naples) from Sorrento.
Here's my photos (include three different trips) https://andiamo.zenfolio.com/p266655284