As you probably know, California includes all foreign immigration - both legal and illegal to boost the numbers.

That way, there is some type of cushion to help against any high usage months, should they just happen to use more than your previous tenants did, or if you unfortunately get tenants who abuse the "utilities included" opportunity. 

How much do they charge and what's included?

Brian Burke has acquired over half a billion dollars’ worth of real estate over a 30-year career, including thousands of multifamily units and more than 700 single-family homes, with the assistance of proprietary software that he wrote himself.

We typically pay somewhere in the range of $3500 for a new, basic furnance, including install, if there are no other modifications to the system required.  

That said, do your calculations for cashflow include setting aside 15-20% of monthly rent for repairs, CapEx, vacancies, etc, etc?

True, but (a) they were typically experienced investors, and (b) today's market includes record prices and high mortgage rates, which is a double whammy. 

There is roughly $20,000 left in rehab including windows, floors, a new kitchen and bathroom. 

that we’ve learned in our 24 years, managing almost 700 doors across the Metro Detroit area, including almost 100 S8 leases:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

A diversified portfolio can include both!