Do the numbers make it profitable?

You might find saturated areas at prices that don't make sense for your numbers (not profitable).

The cash-on-cash return for my co-hosting ones are basically infinite because I put zero down in monetary value (sweat equity and experience are another thing) to make a profit.

You've obviously read renting out properties is easy and profitable - but, have you looked at when the material was published? 

So if you have a business entity other than a sole proprietorship you will file that business return and receive either a K-1 distribution or pay corporate taxes on the profit. 

While the lack of income tax is a huge draw for many, I agree that property taxes can quickly eat into profits, especially for investors renting out properties.

If you sell houses to buy a primary residence you will pay tax on the profit, PLUS recapture the depreciation deductions you will be taking on your taxes each year.

If so they would have sold their house for (ultimately) $75,000 more than they did; received 9% interest (probably as much or more than if they invested the proceeds) on the amount they were waiting for, and if by some small chance the borrower/buyer defaulted, had an opportunity (along with the frustration, cost, etc) of reselling the property and obtaining a “windfall” profit.2.

In this case, your profit will be between 12% and 15% of the ARV.

-> Stress-test rehab/vacancy/hold time.3) Your profit is made at purchase.