How to maximize leverage on 4 SFH rentals to get to that "next step"

[David Gleason]

HI BP community! I currently have 4 SFH rentals in the southeast, 3 of which are owned free-and-clear save for property taxes and insurance. The 4th has a LTV of 40%. Combined rents on the property net roughly $4200/mo after expenses (PM, taxes, ins., etc.) According to market comps from the area all together the homes' value total approximately $600k minus 80k left on that 4th property's mortgage. My main goal is to get to that "next step" and use these assets to leverage 5+ multifamily, apartments, or cash out refi's to spread out into additional SFHs. The problem is that I live in California (which is cost prohibitive for me currently to "buy local") and must rely on remote management that is local to the investment area. I'm saavy enough to know that I don't know enough yet as to what would be the best use of these assets to grow my portfolio and really begin to snowball the passive income, leverage and appreciation. Given the parameters of needing to be remote and trying to maximize monthly passive income while acquiring more/larger properties either through more SFH or 5+ multifams, if you were in my position, what would y'all do? I'm open to "outside-the-box" ideas as well (getting into-self-storage, etc.) Thank you in advance for any and all advice!