When to take the step to next level or go bigger?

[Vitaliy Stolyarchuk]

I became a landlord by chance, and after noticing the potential started expanding on it, having it as my semi-active third income. Bought a single-family house in PA because my full-time job had career potential in Q3 2020, and the rent prices were elevated. A year later, I got a better offer elsewhere and decided to move and buy another single-family more local to the new place, again due to high rent prices. The first I did not want to sell, because it was everything I wanted and thought I would rent it for a while until I move back. Long story short I have 4 mortgages that bring me anywhere from $900-$1300 per month each in positive cash flow. I'm currently renting in a new city while working for my full-time job and am looking to buy small with the same mindset, that if I relocate due to job change or business need, I'll be able to rent it out and have positive cash flow.

I'm wondering at what point should I start scaling up from single-family to multi-family, or apartment buildings, or commercial?

I'm currently at ~1.4 million asset value across my 4 properties and have about $900k in mortgage liability. Locked in at 2.75% to 4.5% across the 4. Have about $200k for down payment with $75k in reserves.

My plan is to buy something for $500-700k to stop paying rent, and then in another year I can buy another single-family and rinse and repeat. Or would it better for me to save more and buy a 2,3,4,5 family while living in one unit and renting out the rest?

I understand there are a lot details left out, and if more information is needed, I'm willing to share. But the question emains the same, at what point did you or would you recommend scaling up away from single-family to bigger real-estate investments?