@Josiah Sia the approach works fine. The slow methodical nature of one property every 2-3 years is what will be hard. Once you start and understand REI and the potential of it, and once you know what a good deal looks like, it will be hard to stay disciplined to your plan and let good deals pass by. Your plan doesn't maximize your return, takes a long time, etc but if you can stick with it the approach will work.
Spend some time understanding how to analyze deals to make sure you know what you are buying and what your monthly expenses are. You won’t net $700/mo/unit after expenses, and if you are buying a 4plex in rent ready condition, as you stated, for $150K that brings in $2800/mo I will venture a guess that the location and your tenant pool will lead to additional expenses. Go on YouTube and watch deal analysis videos or watch Brandon Turner’s weekly webinars, as they are geared for beginners and focus a lot on analysis. Good luck!!