drving Venice --> Sorrento

If you take the route along the Amalfi coast, then yes, you are travelling a rather narrow, crowded road with a drop on one side for much of the way. Otherwise, you will probably fight traffic through Naples and the Amalfi Peninsula. Since from Guilianova you will pass very near Rome, I suggest maybe finding someplace near Rome to drop the car, then take the train the rest of the way into Naples and on to Sorrento.

I have someone telling me the additional drive from Naples to Sorrento is fine since there is a low wall on the right whenver the road gets really high. Is that true?

You can check it out for yourself using Google Maps Streetview. You'll see that in some places that "wall" is no more than a curb with a little hand railing.

We've recently driven the road east of Sorrento, towards Naples. Although it does run along the Bay of Naples for some of the time, I don't recall at all any large drop offs and scary edge of cliff drives. My only recollection is that when you can see the water you are pretty low down. Cheers!

I have drivent that route. I don't think it is that bad of a drive. Once you get past Sorrento along the coast the roads to get steeper and narrower. I did those roads too and my experience was that the first day of driving is definitely a 'getting use to it day'. But once you are use to it, it really isn't that bad. However, I do have a very strong recommendation that you bring your Garmin with the Italy chip. It will save you much time and anxiety. Also, be patient with parking. I think I found finding parking worse than the actual driving.