Downsides for conservative investing?

[Josiah Sia]

Howdy! 

Looking into getting into REI and have been looking at different systems and vehicles to get me there. We don't have any huge goals of owning 1,000+ units or raking in millions a month. Our goal is just to replace our monthly income of roughly $10,000/month passively within the next 10 years. That's it! 

Looking into ways to do this conservatively and one of the methods that really stood out to me was buying a MFH (2-4 units), paying it off, then taking the full rent + savings from our FT jobs and snowballing the same process over and over until our goals are reached. 

Averaging the rents around $700/unit in our area, that would only take 15 units to be fully paid off to achieve $10,000/monthly passive income. We have a decent amount of income since we've reduced our mortgage, auto loans, and adjusted our budget to live significantly below our means. This is definitely achievable in 10 years if we buy 3 quadplexes and a triplex, or 8 duplexes, etc.

I know this isn't the normal investing kind of plan I see out there but this is how we could leverage REI to meet our specific goals to reach financial freedom.

I'd like to ask the seasoned veterans here if there is anything inherently wrong with this plan? Is there anything else I should know about before setting this as "the plan." I don't see this kind of plan talked about very often or at all. Most everyone is looking into BRRRR and other types of trade-up systems.