1- depends on the parts.... if it's chassis parts, check with the chassis manufacturer and auto parts places like Autozone or NAPA For appliance parts, figure out what you need and the manufacturer and google it. For Body parts, you are sort of on your own, but if you search for RV salvage yards, there are about a half dozen large ones that may be able to help
2 - As the previous post said, add solar.... there are lots of experienced solar people on this forum... I'm not one of them
3 - I' not familiar with CA. motor vehicle rules... check with the local office
Good luck on your project.
Joe
2013 Dutch Star 4338- all electric
Toad is 2015 F-150 with bikes,kayaks and Harley aboard