I have been a part-time landlord for a decade (with from 2-8 rental units at any time). Currently, I have a fourplex and two condos (6 units)
I have even owner financed a couple (one fully, one partly) of properties.
I have graduate degrees in law and business and also teach business at a college.
So managing a few rentals while holding down a day job is my specialty and the topic of my first book, just out this past fall:
Every Landlord's Guide to Managing Property: Best Practices from Move-In to Move-Out (Nolo, 2015).