Lesley Resnick There are a number of articles on bigger pockets that do an infinitely better job of explaining GRM than I will, like:https://www.biggerpockets.com/renewsblog/2011/11/09/gross-rent-multiplier-–-techniques-to-speed-up-your-decision-making-part-ii/It's the primary way banks will value your commercial multifamily buildings to determine the loan amount you can take out.

Foundation.Fixing a moblie home is not as expensive as a SFR, but multiply this repair by the number of homes and it adds up quickly.

Multiply that ratio by the appraised value to get the depreciation basis for the rental property.BTW, when converting from personal use to rental use, the value of the property is the LOWER of your cost basis or the appraised value.

In general, if your Gross Rent Multiplier (GRM)  {the ratio of acquisition cost to monthly rent}  is below 50, then barring something outlandish with the operating costs; structure/integrity of the property; a serious defect in title; or local (re)development plans, the deal should be viable.You will still want to obtain actual financials (2 - 3 years) and perform a full discounted cash flow analysis.  

It is based on the price paid multiplied by .02 to get your monthly expenses or what they should be.  

Call it $5710.Subtract annual mortgage interest deduction and annual property tax write-off multiplied by the formula a CPA gave me that includes their top state and federal marginal tax bracket, divided by 12, from it, note that I'm not a CPA confirm with your CPA.

I feel like focusing on one property and paying it down/off is more of a middle class get out of debt/all debt is evil move that my family is advising instead of multiplying and building more wealth.

A way to help the analysis is to also look at the gross rent multiplier for these sales and compare it to your property.  

If you purchased the property for $150K and did not make any improvements, then multiply your purchase price by 80% to determine how much of your purchase price is attributed to the dwelling structure and attribute the remaining 20% to the land value.  

But if you are calculating expenses as a percentage of rent (which many people do), this number doesn't tell you much more than the gross rent multiplier (GRM).