Has anyone rented a car in Rome and driven through Tuscany to tour wineries, have a wine dinner and stay overnight in Tuscany and then hit some more areas of Tuscany the next morning and drop car in Florence?
I've rented a car in Rome and driven to Tuscany many times, but always for longer periods. It looks like you are planning to rent in the morning and returning the car in Florence the evening of the next day. The drive alone, assuming you are not taking the A1 freeway, is at least 5 hours (without pit stops).
Was this a good way to do the trip vs fast train to Florence and renting a car there?
It's a good way to do it, because it's cheaper and faster to rent in Rome and tour from there, since many Tuscan locations people like to visit are between Rome and Florence. However it looks like you have a very limited time. Rental offices open at about 8am. Often there are waits. I've never been able to pick up a car in Rome (or Florence or Bologna or Milan) and drive off the garage in less than one half hour (or a very good day). Car rental returns in Florence close before 8pm. The one at the Florence airport closes at Midnight.
If so where in Rome is easiest to rent a car? We will be staying in campo de fiori area.
I use the consolidator/broker www.autoeurope.com or their affiliate (same company) www.kemwel.com (check prices in both). I always select 'Rome All Locations' as pick up options, as prices vary greatly at different offices on different dates. All companies (Europcar, Avis Budget, Hertz, etc.) have several offices in Rome. The closest offices to Campo de' Fiori would be in the area of the Vatican/Prati or near Via Veneto. But I would choose the pick up location depending on the best price. No matter which office, you will need to get a taxi to take you there. Getting to the GRA (Grande Raccordo Anulare=Rome's Grand Ringlike Beltway) is not difficult from any office. That is where you want to head first to get out of Rome. From Tiburtina station or from Termini station it is easier to reach the freeways. However they rarely have the best rental prices. The Airport has always the most expensive rental prices, if you pick up from the airport.
Any itinerary ideas?
Strada Regionale 2 (SR2 'Via Cassia') through the Val D'Orcia, Siena, and eventually to Florence (via SR2 or via Chianti Road) comes to mind.
Suggestions for where to stay overnight and have a great wine dinner?
Lots of choices, depending on itinerary. Decide the itinerary first then someone will suggest nice spots.