If this is your first investment altogether, I'd opt for a more traditional, simpler purchase. 

You could rent out your current unit and buy another house hack, or even convert the whole property into a traditional rental.

I wondered if SF route might allow us to secure better terms at maybe a 4% interest rate for a few years on the funds not rolled into current $150k potentially assumable mortgage -- and in a few years we could roll into a traditional mortgage. 

Great news is when you get a deal there the spread is usually solid, bad news is many of the traditional marketing tactics don't work very well (at least in NYC where you cant cold call, PPC & PPL is really expensive and I don't know anyone who does well with direct mail).

Instead of leaving equity tied up in the property, you can refinance and put that money to work on your next investment.Advantages:Leverage: You’re using borrowed money to increase your purchasing power.Long-term Wealth: By holding rental properties, you benefit from appreciation, passive income, and tax advantages.Scalability: The ability to keep reinvesting capital makes it easier to scale compared to traditional buy-and-hold methods.Is BRRR Right for You?

Based on my knowledge of the market and similar properties I think these are at, or near, 2X market rent.I've use a traditional bank to finance the purchase of each of these buildings - using a traditional commercial real estate loan.

I've done it the traditional way of using my credentials; credit, job/salary, personal info. to getting a FHA loan.

Come and go because I always based my dreams of real estate off of traditional financing.

A traditional IRA pays taxes when you withdraw month at your normal income tax rate which is generally higher than the normal capital gains rate.

The rental income ideally should cover your expenses, such as the mortgage, taxes, and maintenance, while also leaving you with positive cash flow.Refinance: After the property is stabilized and generating income, you refinance it with a traditional mortgage.