Alternatively, if you're wanting to do something more aggressive, you could consider a balanced fund, such as Vanguard's LifeStrategy Income Fund (VASIX), which is 20% Stocks / 80% Bonds.

It is one of the best examples of City Council and local registered community organizations huddling together to create restrictions intended to thwart development but here they are doing it in a manner which will leave new housing stock in the dust relative to other neighborhoods thanks to terrible design restrictions.

Should I save and pay it off quickly or would the money be better in my pocket or in stock market?

As others said use low money down loan to owner occupy another and reinvest the rest into a another property/stocks. 

You can't buy stocks for a discount just because you don't buy them at the NYSE.

For instance, if you want to do 2-4 units then West loop won't work, but Evergreen Park or similar areas might due to the housing stock. 

To insurance salesman the answer is always life insurance; to stockbrokers the answer is always investing in the stock market; to a hammer the answer is always a nail. 

Back then, BRRRR worked because we could predict future outcomes with some certainty—what a property’s value would be post-rehab and how the refinancing terms would look in 6-12 months.

You can't predict how someone will react to any circumstance.Let me ask you this:Where would you go if you were a hungry lion in the savannas of Africa to find food?

Low risk properties have predictable returns, predictable returns are better than high risk high returns.