I paid cash for the house (approximately $15,000) and then took out a loan from my bank for $20,000.

After bills paid, I typically have around $300 to $400 left to spread out for savings monthly.

We Inherited 2 great tenants who paid on time, no issues.

I personally took the classes to get a license and was planning on actually completing my license, (though never did because I moved to CA), in MA for a few reasons. 1) The cost was low, I think I only paid about $400 for the course.2) The time commitment was low, you only need to complete 40 hours of instruction.3) If I wanted to get a license, I could do so and hang it with a broker simply to help myself with my own process of accessing the MLS and being more self sufficient.Having completed the course I can tell you that you will learn nuances to real estate that you didn't already know. 

And really loved taking advantage of the pre 2008 rules.  

Two of the tenants seem to be ideal with rent being paid on-time, considering it being put in the mail, etc. 

I have paid on them for a year.

As your loan gets paid on time, and you show a positive trendline of increased DSCR I'm sure you can ask to remove this quartlerly requirement.

You will need to combine the knowledge you learn here with your knowledge of your local market, and likely that of a mortgage broker and real estate agent in order to determine your best plan of action.You can call a mortgage broker and find out how much you may get pre-approved for.

I effectively paid little for the illegal units when I brought the buildings (say $200 PSF), but the square footage is good, they have respectable enterances, decent light, amenities, etc. so it’s worth the hassle of dealing with the city.