It is my understanding that you would have to constantly adjust piers under the house to keep the foundation level.  

@David Cole This is a terrible investment with these numbers and you are not even accounting for management, vacancy, and capital expenditures.Learn what cap rate is, find  out what cap rate investors in your area are looking for and adjust your goals accordingly.

I know people want to retire through investing but as a real estate agent I don't see myself ever quitting real estate instead just adjusting my focus. 

Could I potentially adjust the lease so that they pay $100 (or so) less per month and they're responsible for any maintenance issues?

It's possible now to capture leads, BUT it's capital and energy intensive.

However, because the loans are commercial, the due diligence process is much longer and intensive than on a Single Family Property, requiring an appraisal, environmental study, property condition and some other case-by-case reports like Lead Based Paint, Asbestos and Radon.

There are ways to adjust depreciation to your favor.  

So, in your example, its:-PMT(6%/12;15*12;21000)= $177.21Now, you don't know the interest rate after it adjusts so you can't do an accurate calculation.

. $10k loan on a vehicle is too much if money is tight and drain the pool if necessary.Also, I wouldn't assume that when your loan adjusts that the payment will automatically go up.

This one allows me to adjust the 50% ratio (because I do management myself and am willing to do it for free) and allows me to adjust the desired cash flow (also not an immediate factor for me.)