We took a bus from Firenze to Sienna. The best time to visit sienna is during the first weekend of July as the Il Palio horse races are on then and its a mad time to be in firenze on the holiday of San Giovanni.
In firenze, the best pizza is at gusto pizza in san spirito and the best pear cheese ravioli is at the restaurant behind the Duomo – Coquinarius.
The easiest way to move around the Tuscan countryside is to drive. Also, most wine tasting happens on Saturday/Sunday mornings so be prepared to make it an early evening. Sienna with its medieval charm is the beginning of many more beautiful stone structures and villas surrounded by vineyards. while wine tasting pick up the bottles you like as they are waaay cheaper than the same ones priced in the cities.
From firenze if you take a short train ride over to the beautiful cluster of five small seaside villages, you will be lost in the quaintness of this region. An overnight stay in one of the five villages is a comfortable way to go about it.
My favorites were Manarola and Vernazza but maybe your choices differ. Make sure the summer is up as the waters can be cold and can mar an otherwise beautiful beach trip. Trattoria Da Oscar in Monterosso has the best pesto pasta ever!!