Basically OK but you are reinventing the wheel son. These formulas (more complex version of same including tax and depreciation effects) were in Graeme Bethune's thesis around 1980. I used versions of them in my housing work for the government relating to various schemes to use private money for public housing during most of the 1980s.
Anyway you have rediscovered a great truth which hardly anyone seems to believe - that unless net yield including capital gain (after tax) beats the mortgage interest rate (after tax) you are wasting your time gearing. Same applies for equities by the way.
I also wrote a paper in the same period showing the optimal turnover rate for landlords with a portfolio of houses.
Finally - the whole analysis needs to be tempered by risk. Both capital gains and rental yields are inherently more risky than the interest rate so you need a higher rate of net return (something more like the mortgage rate than the cash rate). Gearing substantially increases that risk.
