Start with your primary, rent out any spare bedrooms "house hack"Use that to practice upgrades, kitchen, bathroom, curb appeal... etcNow you have experience as a landlord and flipper, use that to buy a distressed propertyAdd 40% equity to the property through home makeover, refinance into a low cost mortgageNow you are cashflowing a healthy margin on a second property, use that to build equity over time, cashout later and buy your duplex/quad.If it's going to take you 10 years to save up a down payment for a small apartment building, yeah it makes more sense to start growing your portfolio with cheap SFR flips instead.Every market is different, every borrower is different, every property is different, it would be ill-advised to recommend anything without recognizing the individual's nuanced goals and objectives with their next acquisition.

One side is traditional rental and the other side I have furnished and have been renting as STR. 

HELOCs are not my primary business so I don't really look into them too much. 

Few people have no clue what is or how it works, I was just reading today that the cannabis growers that will be trading BILLIONS of dollars in CA, cannot deposit those funds in traditional banks, therefore; many will be using Bitcoins and other digital currency. 

My primary residence is in a trust.  

Living in one unit and renting out the other helps you scale quickly because you need a lower down payment for a primary residence. 

Balancing rental income, appreciation potential, and location can provide a primary home and a long-term investment portfolio.Good luck!

We’re debating whether to sell our first primary residence or keep it as a rental.

If married you can exclude $250,000 each in capital gains if your primary residence.  

Pay attention to whether the room is a primary suite (your own bathroom) or shared bathroom, how many roommates, etc. as those would factor in to how much someone would be willing to pay.