My conviction is that the base formulae, the rent plus utilities (from the worksheet, you are correct!)

I find it hard to believe they (or anyone) have the magic formula to making money and give that data away for free without some hook, so do your research.Talk to hosts in your found locationsLook at Airbnb listings thereUse other toolsEtc.Good luck!

Pay the bill yourself, then reimburse yourself by charging the tenants based on a formula.

Another note to my formula, you need to factor in the amount owed on the structure.The formula assumes 100% free and clear.The amount owed may be split in a different percentage in your agreement than the asset value.You will also have profits and losses and depreciation to split up.As the others have said...attorney.

Is there a number formula like it is with home rehabs? 

There's a formula that you can analyze how much actual money you'll make in 5 or 10 years when combined both things.And also remember: Cash flow is a current state while Appreciation is inherently speculative.I give you a clue.

Des Moines doesn't fit my investment formula. 

If you'd need debt, then things get more complicated and the answer to your question would be: "probably not".If you'd like to learn more about the formulas in the above calculations, checkout my recent blog post: How to determine the value of a multifamily?

That formula has spelled success for a lot of my owners.

I would just go in with my formula.