So for instance, if I have 20% leftover every month, that goes directly to principal. 

I HAVE been wrong quite a few times and, luckily, have been corrected by my colleagues in those instances.

For instance, if the exit cap rate is x, am I still making money?

For instance, if a homeowner doesn’t have the ability to pay for a home, they also lack the funds for necessary maintenance.

no reason to retitle the property. although I think you have the right to do it in many instances. but why ? 

For instance, mileage from driving around to view properties for sale, educational expenses like books or seminars, expenses from networking events with other real estate professionals, etc.Hope that provides a helpful example. 

I would not purchase if net rent was 10% of purchase ($70k in this instance). 

For instance I'm not sure if my cash buyer will pay me the option fee before theres even a title search done.

For instance, today, walking the project I noticed that we didn't address the washer values. 

Long term rentals have the least amount of interaction required, but short term rentals (AirBnB, etc) have higher profit margins - but require a lot more attention (some companies charge 30% for management and the daily turnover service, for instance).I would suggest you compare your potential rates of return from real estate with other investment vehicles.