This thread, and the amazing calculator built by @azdavidr will be a huge help for you on this. Here in the desert, the “Water Use it Wisely” website is amazing.
As for crop coefficients, this is based off the type of vegetation and how well it utilizes the water it receives. There are default values for trees, shrubs, grass, etc. You can adjust this setting to fine tune based on your individual system.
With default values, the system will run, and in most cases, will run just fine, but it won’t be optimal. Same with your camera analogy. Yes, there are a lot of complicated advanced settings, but that is what make Rachio so powerful.
Happy to help you work on your system settings if you would like to share some screenshots of your zone settings.