To answer the OP question, this is my experience as a grower in the greater los angeles area.
There is no "legal" grow option here. Even if you grow on site at a preICO dispensary, you risk police coming in and ripping everything down. The best you can hope for is thats all they do. The worst is arrest or they start investigating you.
Warehouse: Not many landlords are willing to let a grower in. The ones that do, their buildings are usually hard to rent or they will charge you more than $1 / sq ft. If you can find a landlord willing to play ball, expect rent to be $1 to $1.5 / sq ft, 3-6 months of security deposit depending on credit.
Fire inspection: Dont register with the city, dont get a business permit, try to stay under the radar as possible. If it does happen, you will have to tear it down.
Lawyer: waste of money, if the police come, he's not going to be able to stop the shut down of your grow. Best case scenario, you have already paid for legal representation if they decide to go after you
Operations: try to limit your time on site. if you are busted on site, they will arrest you. i have heard of smaller grow ops being busted and only being issued an arrest and released. dont hedge your plans on that. If you run a smaller op (<20 lights) cops probably wont investigate. if you run a larger op, and/or stealing power, and/or part of some other crazy investigation, you will probably have to take a long vacation
Manpower: depends on style of grow, mainly, how many plants per light. You can do 100 flower + 10 veg with 2 people only. However, keep in mind, the more you grow, trimming becomes an issue. With what i mentioned, you need 1 full time trimmer.
Lights: almost everyone in the commercial grow arena is doing 1k watt lights. if this is a question for you, you might not be ready.
AC: in southern ca, you need good ac units. at least 4 months out of the year, they will be running full blast 24/7. 5 tons per 12 lights is a good calculation. look into mini splits, cheaper to install, easier to run, less foot print. All acs are not meant to be run the way we run them. Maintenance them twice a year, expect to replace every 3 years.
Robbery: ive heard of it, never experienced it. All stories i know of, its an inside job. Rarely are people going to be kicking in random warehouse doors to see whats inside. if you can run it with 1 person, do it. if you are going to "hire" a guy, pay him 2k a month and then you suddenly get robbed? thats your fault.
This is based on many years of experience, I got specific stories or experience that has led to the above tidbits of info. Any questions, ask away.