Thank you for all of these tips. We will pore the maps over the weekend and come back with detailed comments [and requests for further advice] if that is OK!
Yes - I am sorry if the itinerary seems hectic. We are in CA for a mere three weeks and we always try to do too much. We thought we had cut it down, but as Roadhound said it will be a good reason for returning.
The Santa Barbara to Sonoma run should be broken up, but there just seems no room in the plan to stay overnight en route, but this is something that I will look at, given the advice. I rather fancy the Big Sur, but it will add a few hours. We will have 12 hours to do the run, so it should be possible.
The Tehichapi trip is a day for me, and we are heading specifically for the loop - I have got quite a lot of advice from railroad forums on where to locate. Speed will be the essence to get there, so it will have to be the Freeway north I'm afraid.
Many thanks - excitement is building.
Peter