I think we have found a place in Bucine to stay for our 4 nights in Tuscany...it looks beautiful. The Montebenichi, however, I cannot get a good grasp on whether Bucine is an okay base in Southern Tuscany. Thoughts?

We stayed not far from there, further south but north of Collona di Grillo (sp?). As long as you don't plan on doing much (or any ) of Umbria, location should be OK for much of Tuscany

Ok great. I think we plan on Montepulciano, Montalcino, Pienza, Sienna, Sam Gimignano, Arezzo and Cortona and Chianti? Sound good for 4 days?

We stayed in Bucine several years ago in an agriturismo for a week. We used it as the base for exploring some of Tuscany. We did have a car and used this to go one day (a long one) to Assisi, another day we just drove around the area and went to a winery. Two days we went into Florence - once we drove to Montevarchi and took the train in and one day we drove and parked outside Florence. We also visited Arezzo (where Life is Beautiful was filmed) and Siena.

I think you've got too many towns listed however, to see all of them in 4 days. Look at viamichelin.com to get an idea of driving times - at least I assume you are driving. But you can always figure it out once you are there and see how much you really get to see. If you are primarily interested in the Southern part of Tuscany (you listed Montepulicano, Montalcino, Pienza, etc.) we stayed in a lovely B&B - La Traverse - and used it as our base to explore that region. Pienza was a lovely little town, Bucine was much smaller - not much there.

We are going to stay at the place in Bucine. It is really lovely and we will have a car so we should be okay to drive around...it is called the Castelletto di Montebenichi...looks really nice so we are just going for it!

We've rented an apartment in Montebenichi. It was 50 meters
outside of the village which is really the hotel plus a small
church. Delightful tiny place - perfect for a honeymoon!

You are out of the mainstream on top of a hill (part of the
charm of the place) so it takes a little while to get to any
'important' towns. We were there for a week so had lots of
time to explore all the other tiny hilltop villages plus go
to Montevarchi to take the train to both Florence and Rome.
In my opinion, you're going to be spending a good portion of
your stay on the road so I'd cut back on a few and save them
for your next trip. Cortona and Arezzo for instance.

The hotel is really very lovely.

WE stayed at this agriturismo a few months ago and had a great time:

http://www.agriturismo.net/castelnuovo-berardenga-532/

We got as far as Assisi but it was a hike. Forget anything south or east of there, for sure. You can reach Arezzo, Cortona and Perugia well enough...