But, they will be in challenging parts of town where realistically you do not want to own property and your long-run returns will under-perform.I'd encourage you to find a balance of sub-market growth, nearby employment, strong income, and only then a good rent-to-value ratio. 

The great thing about living in a high cost of living area is that your salary / wages are hopefully also very high.If you are a new college grad, I would focus the next 1-3 years on increasing your salary as much as possible(gain new skills, new certifications, change employers, etc).Once you make more money, you can easily get in a position to buy a property on a more frequent basis.Best of luck!

Leverage magnifies return. 3) The effort involved in adding an ADU is comparable or larger than a rehab associated with a BRRRR.

Is this a realistic path to reasonable CoC return? 

Sometimes an $800k 4-unit could be a better return than a $300k 2-unit...or visa versa. 

Those types of properties can bring in good returns, but the management can be intensive, and finding reliable tenants for both residential and commercial spaces might take some work.

I would lean towards recommending that you pursue the deal - plus having the property remain in your family may be a net positive for you and your extended family regardless of the ultimate financial return. 

Generally speaking, if you borrow money at 7% interest and your investment is earning a 10% return, 10% - 7% = 3% and you are not growing faster than inflation.

Here’s what I’ve learned so far: Investors want deals with solid profit potential—so they’re always looking at the numbers: a good ARV, reasonable rehab costs, and enough room to make a return.

Also -without an in service rental, you have no schedule on your tax return on which to deduct those expenses.