Roberto, this is helpful!
If I get a car in and out of FCO, I would instead return the car on Monday AM before my afternoon flight. I would hope to return it around 10:00am on a Monday - my flight is at 1:40PM. If returning the car directly to FCO I would not need to stay in Rome for my final night in Italy
It was a nice idea to spend one last evening in Rome, but I'm finding more time on the farm is preferable for my hosts. But it might work out better to return the car directly Monday AM and avoid train transit all together as much as I prefer it to driving.
So this potential new plan would mean I rent a car from FCO on a Friday afternoon (ugh - that might be tricky? Likely around 2:00pm hopefully not later) and drive up toward Arezzo. I would drive back down to FCO on a Monday morning, arriving in Rome around 10:00am.
My last dilemma is to get Manual vs Automatic. I was quite good at manual in my 20s, but it has been many many years. I'm a little nervous about doing so again when by myself in a City I don't know that well (only 1 visit so far). Should I suck it up and pay the extra for automatic?