you'll love the area around Monticiano
Ciao Barb and welcome to our Forum!
You'll be in a great area in Monticiano - we were there last October and loved that whole area from San Galgano to Paganico. The abbey was spectacular, and we highly recommend visiting
Roccatederighi and
Montemassi if you can.
If your group is into hiking a little bit, you can do the walk from Monticiano to the Abbey - it takes about an hour each way, all pretty flat. We also loved the short hike up to the ruins of the castle above
Sassofortino through the chestnut forest. It really was a short hike and what remains of the castle is impressive; it was a nice stop near Roccatederighi.
With such a large group, you'll be fine with the outdoor visits to villages and shops but you definitely need to look into the meals and winery visits. For meals you might just need to reserve a day or two before, but for the wineries I suggest contacting before you arrive to set up a dedicated visit/tour.
Many of the restaurants we ate at in the area had large dining rooms so I don't think your group will have difficulty. Many are connected to "agriturismo" facilities - basically along main roads in the countryside and not necessarily in town. You'll see these as you move around, so keep track of them.
In Monticiano itself we ate at "
Da Vestro" - it has a large dining room plus a large outdoor dining area. It is also a hotel if I remember correctly. For your first day it would be perfect since it will be nearby and you won't have to worry about finding a place to eat.
We ate there for lunch so we only had a pasta dish and dessert - our pici all'aglio and tagliatelle al cinghiale were both delicious

Basically good local and Tuscan food. Found a site -
http://www.davestro.it/ Tel. 0577 756618 / 756566. We remember also seeing a pizzeria in town which is another place you should try.
That day we had first tried to eat in
Iesa, a few kilometers from Monticiano, at the
Aia di Gino. Supposed to be a really good "slow food" restaurant with lots of home made dishes but it was closed! It must have been a Tuesday as I see it is their closing day here:
http://www.sangalgano.org/ristorante_aiadigino.htm
At the bottom of this page is a list of the restaurants and pizzerias in the area:
http://www.sangalgano.org/ospitalita_alberghi_ville_agriturismo.htm
I am not sure of the total space available but we loved the
Locanda nel Cassero in
Civitella Marittima.
http://www.locandanelcassero.com/ Tel. 0564 900680
In
Roccatederighi try
Garum and their "garum" pizza, really interesting flavors based on an "etruscan" sauce - Tel. 0564-567 445
As for
wineries - there are so many it is hard to recommend one in particular. First, stick to San Gimignano and the Brunello and Montepulciano wine areas as they are closer so you'll have less driving to do. Having said that, start by looking at some of the places suggested here:
http://www.discovertuscany.com/forum/general-tourist-info/83-wineries-ourselves-rented-car.html or here
http://www.discovertuscany.com/forum/general-tourist-info/123-any-ideas.html .
Do you have a particular wine/winery you like and want to visit? That is usually one good way to start, to look for an estate that produces a particular wine and visit them. Or you can consider contacting a tour guide and getting them to organize the visit for you. One example is this one:
http://www.enjoyflorence.com/english/Wine_taste_Agriturism.htm which offers several tours, including one at the
Castello di Verrazzano in
Chianti which can include lunch or dinner.
Knowing the name of the estate, I found that you can book a tour directly:
http://www.verrazzano.com/en/index.php?c=visiteguidate
For Brunello, two of the better known estates are
Castello Banfi - you can read more at
http://www.castellobanfi.com/tour/ - and
Il Greppo - here is the link
http://www.ilgreppo.it/wine_tasting.en.php
Hope all this information is useful, let us know if you want us to provide more suggestions for a particular place. I am sure you will all have a great time in the area you'll be in

!