Some things to think about: Cali requires class B license for the 939 series. There's lots of good trucks available in SoCal. Actual performance differences between A0 A1 and A2 under any conditions you'll likely find while playing with it will be minimal. Choose what appeals to you. CTIS looks like a very good idea in theory, but in reality tends to be problematic.
As mentioned above, making changes after purchase is much more expensive than finding the truck in the config you want.
Mileage: expect 6ish, with the turbodiesel doing a bit better. That being said, I recently drove one from Houston to Tulsa and got 13mpg. I'm shocked speechless. The only other explanation of the mileage is someone sneaked diesel into the tank when I stopped for the night, because I refilled it until the strainer was showing fuel before I left Houston and exactly the same on refill.
Screen the truck if at all possible. If not, make sure you go over the video and pics with an eye for detail, and realize you're rolling the dice. I bought a truck described as 'starts with a jump' and figured I'd immediately have to spend $800ish in batteries, only to get there to pick it up and find that it started easily no jump required and had 4 batteries dated 11/2012. It could just as easily been the opposite: the truck described as 'runs and operates' may surprise you with a rod knocking...
The following items generally increase price by the following amounts, these being just my observations: winch $1500-2000, A2 $1500, A1 $1000, A1 with the PTO console but no winch $1500, canvas and bows $600, hard top $400, dumptrucks bring double, and location makes a big difference in prices. Fortunately for you, from what I've seen southern Cali is full of high quality rust free trucks for lower prices than found elsewhere.