Joe,

I drove along the same paths you mentioned just this last November. Not much to worry. Just take care that the lanes are noticeably narrower than the typical US highway, pay attention to the signs at toll stations (I stuck with cash and followed the signs showing a hand and coins). Always keep gas filled to at least a quarter of the tank.
The roads to SG take you over the hills and through the fields across the farms. It is gorgeous and plenty of olive farms and small wineries. Driving in the hills after dark did get a bit dicy.