I saw some interesting single family houses (newly constructed) in the range of 200-300K, for examle in:McAllenEdinburgSan JuanMercedesHow can I deep go into research about those cities and neibarhoods in term of demand for rentals and for sales?

I haven't started my investment journey yet, but I am interested in Fix & Flips and short-term rentals. 

I have since found that the best long-term return is created through passive income with rental houses.  

My goal for the next 10 years is to build a sustainable and profitable mortgage business and use the profits to invest in long-term rentals.

There is some nuance there that your accountant can assist with but in terms of asset protection truthfully nothing to be gained either way.

The cost of changing a light bulb is quite a bit more when you factor in travel time to get across town, vehicle cost, a qualified person on payroll with benefits, overhead cost for the office to deploy that person.

It's true you'll likely make very little money on those deals but your benefit will be expediting the pace at which you learn this industry.  

I work in Real estate and have broad experience helping expats and investors to find the best properties that suit their needs. 10 years ago, anything you could buy was a great investment, in terms of return, valuation, and resale opportunity. 

Hello Shad,I think there is always a time and place for flipping, but I think you build long term wealth with buying rental properties. 

Without more context, it's impossible to know whether the owner financing terms are reasonable or "ridiculous."