In addition to STR'ing the main house, he is building 2 more units (ADUs) on the back side of the property.

would you rent out your property to a problematic tenant who has a good rental history which means always pays on time with a good credit score. i'm in the process of renting out my house

Quote from @Simone Montague-Jackson: You can house hack with up to four units.

I just bought 5 houses in 5 days in 3 states, 1 of the states I never bought property before. 

As a broker, you’ve already got a strong foundation, which will give you an edge in finding and structuring great deals.Since you're in Chicago, have you considered house hacking as a starting point?

High demand for Section 8 housing.

But to answer your question, House canary is good for rent rates, zillow is a good tool for property data and for seeing what is for rent for how much, sales comps etc. 

You’ll need to handle inspections, work with housing authorities, and make sure your tenant screening process is solid.

If you are single or a couple on the same page about house hacking, look for uneven multis.

@Derick Jennings Without knowing more about your situation, I'd likely recommend a house hack, a strategy I wish I would have known about when I got started.