Most has been covered. If you’re confident I’d say a car is definitely preferable with the freedom it affords, but obviously finding parking in some places is ballache.
+1 to don’t bother with Pisa / if you’re over that way you can do the tower in a morning and then get the fuck out.
I stayed in a beautiful converted castle/vineyard near Gaiole called Castello Di Tornano, but there was Castello Di Ama and Castello Di Meleto which were both bigger and nice to get a look around (Meleto especially) should you decide to venture a little in to the Chianti region. Beautiful, breathtaking scenery in the area as well, kept pulling over to just stop and enjoy the views.