Where are you based out of? 

Look for properties with low taxes, separate utilities, strong demand, and potential for rent increases.

There is still strong demand for Austin housing with pending sales in the metro up 16% compared to last year (and up nearly 30% in Austin).

3 recent national studies show that the rent to value ratio is at an all time worse (what they really studied was cheaper to rent than buy, but there is strong correlation).  

Since you have no contract, there is nothing that says you do not have to pay if you are not satisfied, and your spreadsheet would seem to indicate you owe him the money.Similarly, since you paid him for previous work on the spreadsheet, and the spreadsheet shows you owe him for additional work, your argument is not very strong.

Not at all.... the rent is based on the market rate, so if the units are all different...size/location/lay out/age etc etc... they would have different markets rates.

You just discriminated against them based on family status.It's good to have a heart-to-heart talk with them about what they can afford and see what they want to do.

They already have a track record (good or bad) with you, so you can decide based on payment history, inspections, etc.

I built this budget template based on my research but am only seeing bad investment returns / don't really know what I'm doing and would appreciate any feedback you all have to offer.

Based on your assessment, it feels like the only way for you to buy something now is to make a compromise that you don't want to make or to get out over your skis a bit more than you'd like. 20 years from now, it won't make much of a difference whether you bought something today or two years from now.