, but it's practical. --- I'm not trying to be negative on any of the options btw, just realistic.

As you get further away from standard real estate practice, the risk is increased by a “legal” risk that your protection may be interpreted quite differently than you expect by a court and that the subtleties of the protection a mortgage or trust deed document provide with established law and court decisions handed down for (in the U.S.) 250+ years is not existent. 

Are you working for a firm in southern California or do you have your own practice?  

Ensure all your screening practices comply with Fair Housing Laws and other legal guidelines to avoid potential legal issues.Improving your tenant verification process can help you find more reliable tenants and protect your investment.

My take is that predatory practices and threats must be controlled, and housing quality must be enforced.

But, is this practical for you and your team if you have 50 properties?

I would suggest watching some youtube videos, come up with your own variation of someone elses script and practice it until it sounds natural.

In reality to be successful in real estate you need knowledge of real estate principles, real estate finance, real estate law, and real estate practices.

Are there any particular management practices or tools that have proven effective for rent-by-the-room setups?

100% financing is possible but not practical.