I'd suggest taking the high speed train from Venice to Florence - the Frecciarossa is really nice, and fast. Then changing trains to a regional from Florence to one of the towns connected by rail. To really get off the tourist path, you will likely have to find a town that doesn't have a train station. I can recommend a driver in Florence if you want to do that.

Tuscany as a region is really well-marketed to tourists, so you're really not going to find a lot of small holes in the wall, but as a starting point do some research on Montefollonico. That might be for you. It's not un-touristy, but it gets relatively less traffic while still having some places to stay and restaurants. It doesn't have an English wikipedia page of its own, so that might be a good sign for you Transportation would look like this - http://www.rome2rio.com/s/Venice/Montefollonico