However, San Diego is an extreme case.However rents increase fast in San Diego.  

He abandoned trying to scale.Learning from this experience when my partner and I decided we wanted to double our net income, we realized it would take a increase of 2 1/2 time our volume and probably need to triple our deal flow.  

You already mentioned Mid term, which can be a great way to increase cash flow.

The 401k is a valuable asset but its my thought that I can use this asset to further increase my portfolio by putting that money to better use.

Who cares about lifetime interest costs, except to the extent you can easily lower them (refinance to a lower interest rate) to increase your cashflow.

You can find SF properties that already have in law suites, garage units, etc, and now legally rent those, so it should increase the appraised value significantly.

The first couple is a no-brainer.The second group has too many people, increasing wear-and-tear on the home.

But if you can finance a home in an appreciating area make it breakeven and at some point (as always) either rents/nightly rates will increase, interest rates will go down, or both. 

If you generate enough money annually to dismiss a W2, then consider covering the ever increasing costs of retirement & health care and those do not go at inflation metrics but usually way higher. 

*As a side note, I think maybe it would be fun also to try and identify where new technology or machine-learning driven approaches could increase efficiency in the spaceAs for my financial situation, personally, I have around 50k saved but 20k of it is tied up in assets I don't want to pay capital gains tax on.