The most important thing to do is make sure to buy at the right price and maintain sufficient reserves to do preventative maintenance. 

Or should capital always be my first priority to prevent people from taking advantage of me?

Go over exactly what frustrated and drained you the most, and think about what you could do to prevent it next time.

You may want to consider the near South Side versus the far southside.Regarding getting taking advantage of, where a property is located won't prevent getting taken advantage of.

This actually aids in preventing fraud vs the mortgage system.  

Defect in drafting - possible if something has clogged the exhaust vent.

Made typical mistakes of most 1st time investors - Overlooked some big-dollar repairs that had to be done after moving in tenants, such as A/C did not work, the hot water lines (galvanized) were so packed/clogged, they had to be replaced, the windows are original - from 1921 - I will be replacing those next year, as they are painted shut...Also - snake the main drain before the tenants move in.

What are others doing to prevent them from freezing?

Manny lessons learned on this project, but I think a big one for me was the importance of not having too many bills that clog up your time with stress and lost time.

Manny lessons learned on this project, but I think a big one for me was the importance of not having too many bills that clog up your time with stress and lost time.