Easiest way to look at this generically would be:Proposed mortgage payments + any other monthly payment you haveYour monthly income + 75%*long-term rentsThis always needs to be less than 50%, and of course other factors would influence your ability to qualify but this hopefully will give you a way to guesstimate the feasibility. 

This also serves another purpose, banks require a PSF to approve you for commercial loans hence having this document completed aids in your ability to be approved for loans promptly.

With rental properties (assuming your using leverage), you receive the benefits of increasing equity (forced savings via mortgage reduction), ability to lend against the asset, tax benefits, depreciation, cash flow, and possible appreciation to name a few. 

Thank you for your reply Seo.

Quote from @Seo Hui Han: What city/market is this car wash in? 

 (2) state of the economy. even @Jay Hinrichs and myself lost money in 2008-2009 LOL(3) Competence and ability of the investment advisor/manager

Those who have yet to buy a home (millennials and younger) are going to get completely screwed and have little to no ability to build wealth on their own through real estate due to cost of housing compared to incomes and the only way they will be able to do it is from mommy and daddy hopefully having significant equity in their home.

This may affect your ability to get credit.

You're ability to manage is what will make or break this.

Taking way your ability to contact the tenant eliminates your ability to keep the PM honest.