Goal is FI by around age 50. 2 boys (5yo and 7yo). 

Hey David, I would say this largely depends on how many units you have, the age of the building, and the quality of the building/neighborhood. 

Quote from @Jacky Johnson: Set up some anti-barking devices: https://www.amazon.com/coprisin-Control-Devices-Deterrent-Ef...I bought these for my dogs.

Age?

., Inspect Mechanical items, Water Heater Age, Roof, and Appliances. 

In New York City, it’s the law to have window guards for an apartment if a child below the age of 10 is living there.Is taking out the window guard and screwing in the air conditioner in replacement of the window guards an option?

In this day and age it is almost impossible to be invisible.

The way I did this, and I started at about your age and with a wife and 3 kids, is I learned quickly that I need to buy out of state.

Previously , Hud's  aged inventory would manually review and accept bids significantly below this threshold -Price drops are not following any specific pattern based on days on market. 

Some things to consider are the age and condition of major systems like the roof, HVAC, and plumbing.