We've completed a HELOC loan, invested through a SDIRA, completed two 1031 exchanges, and we just now are doing our first cost segregation study on our portfolio to reduce our 2020 taxes to zero even though we made over six figures! 

Once you do enough deals in a particular market you will likely be able to figure your costs pretty quickly.

It would also cost about $5k per unit to furnish it - this isn't that big of a deal but it is worth considering.What would you do?

I would think of this problem differently: I might encourage them to explore ADUs... this would give them an additional stream of income and would likely only require a relatively small chunk of money in their savings (relative to the total cost).If they could partner with someone that has experience building and/or flipping (to qualify for the construction loan), then cash them out with a 30-yr DSCR loan (and use that as the builder's profit), then they could rent the property and enjoy the cash-flow.

You never know when an accident will happen and for the few hundred dollars an umbrella policy costs , it’s worth it.  

(It is more costly though)     I gave my cpa my income & expenses per property he said that’s not enough.  

Being specifically located in CA could help marginally, but you may also pay a much higher fee due to the higher cost of living (depending on which part of CA of course).

Be sure when you are mathing out your next purchase, you include the cost of the HELOC. 

Taxes and insurance costs are "covered" in the rent.

The cost of entry is low, and cash flow is high.