Driving Amalfi coast and driving Florence to Positano

You will need a car in Tuscany, especially to get to a villa out in the country. And since there are four of you and you will already have the car, it would probably make sense to drive it down to the Amalfi Coast region. But once there you don't need it. You can get around the area by bus and boat and parking is horrible. Although depending on how much more it will cost to keep the car for your time there - you don't say how many days you plan to be in the AC area - it might make sense to keep it but not plan to use it every day. So for me it would depend on if the accommodation I wanted had parking, and how much per day extra it was going to be to have it. If the total cost for the car rental is not much more for the entire time than it is for the Tuscany portion, and if you find someplace to stay with parking then I would keep it. Otherwise no. But even if you keep it maybe plan to use buses and boats to get around at least the major towns down there.

No way would I ever want to have a car on the Amalfi Coast - and I'm not easily intimidated. Just too much stress from the traffic, and twisty narrow roads clogged with crazy drivers. A car may be fine in Tuscany (no sampling wine and then drinking, of course). Along the Amalfi Coast, leave the driving to professionals and sit back so you can enjoy the scenery.

What about the drive from Tuscany to Positano? Since we have four of us and will already have the car, does it make sense to do the drive instead of train?

Not to me. I'd drop the car after you're done tooling around Tuscany, and take the train to Sorrento or Salerno, connect to your target location (Positano or wherever) on the AC from there. Personally, I would not proceed beyond Sorrento or Salerno by car (unless I got someone else to drive it). I greatly enjoyed being a passenger on that road twisting along the cliffs, but I was very glad to not be behind the wheel there. And I'm generally up for some pretty challenging driving.

Is the car a benefit or inconvenience for Positano and the Amalfi coast?

Definitely not a benefit; 'inconvenience' is way too mild a term to describe the negatives.

You are planning to be in Rome the night before your flight? ( Hint: the correct answer is 'yes;)

One of the key points to understand is that you simply cannot use the car for local transportation IN the popular towns on the actual AC. There are only a handful of street spaces, and there aren't that many pay garages. It's much worse than a downtown major city, for example.

In late May and June, if you have a car, you'll spend many hours in it wishing you didn't have it. You'll be stuck in traffic going anywhere and then you won't have a place to park the car anyway. The road along the AC is a narrow 2-lane road which hugs the cliffside - that means lots of curves and up and down as you creep through the villages. Some of the bus stops are right on the road, so when the bus stops, everything behind it does too. Along with the public buses, there will be lots of tour buses and vans.

In the best of times, driving that road is challenging. I did it in February, when there was virtually no tourist traffic and while the speed limit is about 35mph, I rarely got above 25 and didn't visit Positano because I couldn't find parking.

In many ways, I prefer Tuscany to the AC, but that’s very personal. I only say it to help you understand that those two stays are not comparable in any way. It’s like comparing a visit to Bucks County PA with a visit to Fallingwater at the other end of the state. (Your visible profile omits your home area.)

If you think public transportation is for losers, you can certainly drive from Chianti to Positano. But every nice site along the way will be 20 minutes each way off the road, and your last two hours in the car will be average speed 10 mph. From Chianti to Naples, it’s all anonymous divided highway. From Naples to Positano, it’s like rush hour in CA or NYC.

In fairness, many people chose a car and driver from Naples to Positano. That’s because the trip to Positano is so tedious by any means. But the rental car has no utility once there. Have you checked how far it is to your Positano hotel from the nearest road?

Isabel gave you the best advice. You will need the car to drive in Tuscany. Also 4 people traveling together with substantial luggage (I presume you will be carrying also more formal clothes for the wedding) will find it more convenient to drive to the Amalfi coast than to carry luggage on multiple trains and buses (or boats).
Therefore in your shoes I would keep the car and drive to Amalfi Coast. Once there you might find it more convenient to keep it parked at the hotel (or parking lot) and use public transportation (buses and boats) to visit the coast since the traffic is often heavy and parking is scarse. Using Private drivers to drive around is an option that is however very expensive.

You will also find having the car convenient to drive back to Rome. However keeping the car parked at the AC will cost you €25 a day plus the rental charges. As such, depending on the number of days there, you might find it cheaper to return the car in Sorrento or Salerno after dropping off luggage and passengers at the hotel (then return to the hotel by bus). However Don’t underestimate the cost of using private drivers to Naples and trains to Rome for 4 people. That will greatly exceed the cost of parking and additional car rental days.

Regarding the difficulty of driving on twisted roads, you are from San Francisco not from the flat Midwest, therefore you will not be scared by the Amalfi coast highway. All you have to do is drive from Redwood City west on Highway 84 then from la Honda to Pescadero (which is worse than the Amalfi Coast) or any roads on the SF Peninsula or Santa Cruz mountains, and you will have enough training to drive on the Amalfi Coast.

https://oltreleparoleblog.com/parcheggi-a-positano-costi-e-info-utili/

Above is list of parking lots in Positano. (Google each for individual websites). The cost varies according to size of vehicle but are generally €25 a day and above. Many hotels have arrangements with some of them, so check with your hotel.

Thank-you! Some very good suggestions! Still haven't decided. After the first comments we thought we would take the train to Naples where our hotel offers a pick-up service for 130 Euros. Then looked at all of the connections needed and time it all takes. Still undecided, but we may drive to Naples and drop off the car there. But, as one person said, we are used to driving on narrow, steep, winding roads along the California coast and mountains so that part of driving the Amalfi Coast doesn't sound too intimidating. The traffic does. And am still checking costs. We can drive to Naples then drop off the car and have a driver take us to Positano. For the return, driver can then take us back to Naples for a train to Rome--sounds convenient. However, it may actually be less expensive to drive to Positano, pay the $25 Euros per day to park (hotel has arrangements for parking) and keep the car to drive back to Rome. Looking for ease of travel and fewer headaches even if it costs a little more. But definitely sounds like we will use other transportation along the Amalfi Coast and don't need/want the aggravation of trying to drive ourselves.

we may drive to Naples and drop off the car there

Drive to Salerno to drop the car off. Nobody who's so afraid of traffic should drive in Naples while on vacation.
Then take a travelmar.it ferry from Salerno to Positano.

If your hotel offers a pickup service at Naples station, remember that going by train is much faster than driving. We are talking three hours v. almost six.

To be clear: I don't think anyone should be afraid to drive on a road like the one along the AC. The road itself is perfectly fine. It's the overwhelming traffic, other driving conditions, and the various "tricks" used by locals to deal with it that makes it not worth the trouble.

The cliff-hugging roads along the California coast (like those we have in my Pacific Northwest home) are beautiful, stunning and fun to drive - but only if you ever get the car out of first gear. When if you add bumper-to-bumper traffic, frequent periods of just sitting stuck in unmoving traffic, and other human-caused conditions, then it takes all the fun away and turns it into a painful chore. At least to me.

Unless you can do it when there's no traffic (6 am on Christmas morning?), you don't so much drive this coastline, you sit in your car on it. Personally, I love a nice drive, but I would rather be a passenger in a big bus on this road - you sit up very high, with a great view, and you leave all the driving worries to a professional who knows every corner, how far into the road every rock and bush extends, how wide every car and pedestrian and trash can is, and you as a passenger don't have a care in the world. That's different from driving on any scenic stretch of the Pacific coast in the USA that I've ever seen.