Wow, that sounds like an awesome ride!

I would be careful with the back thing. Backs are very tricky and they can take a long time to heal right. But assuming you keep training with no significant discomfort, the mileage and challenge will be amazing. I don't live in CA but I've been fortunate to drive around Carmel and Big Sur a couple of times and that is some amazing terrain and vistas. You do not have to ride fast to enjoy the scenery, right?

Good luck and always put your health first - if your back or something else is causing you worries there is always another ride some other time. But if you feel healthy and ready for it, you probably are so enjoy!