The math was a no brainer and bought 2 duplexes from him, purchase price of 67,500 with rent income of 1750 each month total.  

Not sure I follow your math . . . but it IS late here

I suggest you use the process I gave above as an example and just do the math yourself. 

Since Oct 2015 there have been 130 homes that have rented for 2500 or more within MLS area 10,12,13,14 which covers spring and also some parts of The Woodlands, cypress, and humble.I did some quick math- I'm interested to know how you come up with 15k in profit...I think there is a little more room in that deal, closer to 20 or so.

Even cap rate math seems challenging (<5%) given how high property taxes are here (and I'm hearing they will continue to increase!).

The square footage in that 2nd bedroom, if you were to do the math such that you isolate just that component, was >75% more expensive. 

If the unit is a 2 bed 600+ then leaves me approx 9134.00 if I did math correctly on the fly on break at work.

Just keep focused on your goals, the math involved, and you'll be well on your way to those goals!  

Then do the MATH. 

Where did you learn math