Southern Tuscany on Honeymoon
Sounds like you have the perfect mind frame for enjoying Italy and Tuscany - SLOW!
7 days in Tuscany is a good amount of time, seeing as you've already been to Florence and Cinque Terre also makes it possible to focus on getting to see other areas in Tuscany.
As you're arriving and leaving from Rome, it makes good sense to focus on seeing the area between Siena and Arezzo and southern Tuscany in general (which is the area around Montalcino).
There are some great suggestions for winery tours by Mathieu here:
http://www.discovertuscany.com/forum/general-tourist-info/277-our-trip-italy.html
as well as here:
http://www.discovertuscany.com/forum/general-tourist-info/83-wineries-ourselves-rented-car.html
Most wineries that offer tastings do so together with some light snack or tastings of local products such as sliced meats or cheeses. This helps so that you can get behind the wheel afterward. But if you don't feel comfortable with that, the area of Chianti and Valdorcia are not that easy to visit by train or bus. Chianti is a bit easier - you can read our recommendations here for moving around in Chianti:
http://www.chianti.com/moving-around-chianti/tips-getting-around-chianti.html
as well as this one about doing some wine tastings from Florence by bus:
http://www.discovertuscany.com/forum/moving-around-tuscany/205-getting-around-chianti.html
I highly recommend looking into doing wine tasting with a group where you don't do any driving. Every Thursday Florence Chamber of Commerce organizes a
wine tasting tour in Chianti by bus, including visits to
artisans' workshops. We did the
wine tasting tour in October and it was nice.
In
Montalcino Vinarium organizes
Brunello cellar visit and wine tasting. Brunello, as well as Chianti, is the most famous wine in Tuscany and is produced in the area of Montalcino.
Not too far from Montalcino (about 25 miles) stands
Chianciano Terme. It is a famous thermal city in southern Tuscany. Etruscans and Romans used to relax here. There are 5 different types of thermal water, each one with unique characteristics. I think it can be nice having a fully relaxing day in a SPA in Chianciano.
Even though you don't intend to rent a car, I strongly suggest you considering doing so. Moving around Tuscany without a car can be a challenge even though it is possible to move around just by bus and train. The thing is you risk spending a lot of your time waiting according to their schedules. Consider that some of the most beautiful towns and villages, as well as a good number of wineries, aren't easily reachable with public transportation and therefore renting a car makes practical sense.
On the other hand, I can understand your worries about driving in Italy. Italians drive fast and roads often wind a lot in Tuscany, but that's Italy and its beauty, don't you think?
I hope my suggestions help you plan your honeymoon trip. Don't hesitate to ask any other questions.