Additionally, and importantly, I’m not buying large apartment buildings so the effect on my and my clients’ portfolios will be muted.

Sounds like an opportunity if other PMs are not good there.One additional point on delegating and vetting your team members.

IMO, you do need to spend time with people more experienced than you.

I need additional funds to finish my basement, and to start builiding a new house on the lot next door to my present three family.

This is the best $50 you'll spend as a California landlord: https://store.nolo.com/products/nolos-california-landlord-bu...You can also join the California Apartment Association for training, forms, and even legal help.

Best thing to do is spend a few bucks and get some drawings done so you can get more "hard" numbers.

Save up the rent money from the house hack (or start now if you already have the cash) to finish off the basement into another rental unit (if zoning allows) or additional square footage to the current property.

Renovated each unit as they opened up which created additional value through increased rents.

If you add additional bedrooms, I would also consider the bedroom-to-bathroom ratio so you don't have too many roommates needing to share a bathroom.

These are professionals with additional training and a stricter code of ethics.