Louis City, storage in these older properties is quite limited and there seems to be a solid demand for extra storage units. 

Not unless the local city requires one, which is rare.

Since the HOA already foreclosed, their lien no longer exists and the 1st foreclosure action will wipe out anything else besides taxes, IRS, county/city fines or levies, etc. 

I've found another property that I feel confident will bring me a similar return as the first (same city, about 3 blocks away, similar price, similar SF, same Bedroom, more baths), but I'm not sure I should buy 3 properties within 1.1 years as it will make me leveraged to the tune of about $550,000.

Many Chinese invest in real estate in "empty" cities in China that inflate the value of those properties.

@Renee Burke there are a few good deals on the market but why the northwest part of the city?

Most cities zone the same way, think of this as a circle moving inward starting at the outside: industrial, commercial, retail, commercial multifamily (huge complexes), residential multifamily (4,3,2 units), single family residential neighborhoods.

. :-)We purchased our 1st STR in Summit County, CO in 2012 and since then have bought a new STR property every 2 years since, with the exception of 2017 when we bought a home in the city in VA where our alma mater is located.

The unit is currently zoned under multifamily-residential (2-4 units) and the City is planning re-zone the parcel into Commercial Office in 2019 (Up to 3 Commercial Offices).

Phoenix seems to be the testbed for these companies before they expand to the rest of the country, so if you don't have them operating in your city you probably will soon.