I'd focus on the BP House Hacking book, it's pure gold man! 

The investor in my case is purely passive. 

Meaning my pure cash flow will end up somewhere around $900-$6,000.

I’m considering buying an STR property with a land contract (also known as an executory contract or contract for deed) with 0% interest payments … meaning each payment would be pure principal pay down.

Where we are ahead, is this is a pure cash play with no debt, thus no holding costs (yes opportunity cost is missed but let's say 3%). 

Normally if you follow a pure spreadsheet model you will get a house with a funky layout that isn't easy to change in a area where tenants aren't ideal.

To my understanding (having had some conversations with underwriters from several different companies)  there is nothing different between the coverage offered by Proper, Foremost, CBIZ, Allstate, Progressive, Travelers, American National, Liberty Mutual, Pure, or any of the other insurance carriers.... in fact the underwriters, E-suite, and actuaries from all of the companies hop between one another every few years.

Real estate is not purely a numbers’ game and there are a lot of trouble owning OOS properties which will eat up all your time(you make good money at work so you know how much your time is worth).

Their RE markets are purely speculative and only driven by investors like you who are getting pushed out of primary markets. 

Whether you decided to save up more capital to acquire more rentals purely from disposable income, whether you pull a line of credit or loan from your free and clear rental, or your primary residence I’d first identify what your end goal is and figure out what that looks like before you decide how.There are many ways to reach that vaunted 10k per month income figure from rentals and some are quicker and some take 2-3 decades.