Hello:A little crash course on risk. essentially a risk free longer term say 30 year govt bond is about 3 percent, if they make even a 30 year cd it would be the same.

Essentially you are buying the right to become the tax collector and collect the taxes and penalties. 

This is essentially the same as acquiring an option to purchase a company's stock or a commodity.I would recommend having no performance ties between the two agreements and would stay away from inflating either the market rent or the purchase price of the property and applying/rebating a portion of the rent towards the purchase price of the property.  

I couldn't afford it, so I did a little research and some creative thinking and I came up with the idea of leaving the original windows, and essentially building another window behind the original window using Plexiglas.  

You'd probably have to look for a hard money lender and pay a really high interest rate, essentially you're looking to buy a building with "No money down" which is not practical.

This is essentially what we have done, except we decided to invest in Summerlin, as I found a place I liked the neighborhood and I could get better price per door.

Essentially you will pay more up front to get a lower interest rate.

Or, essentially, what am I doing wrong or not understanding which is holding me back from expanding further and faster on new opportunities due to my reluctance in taking on any debt?

Then the seller essentially is both the Seller and the bank (2nd position) lien holder at closing and then all the money is held with the QI.  

If the borrower chooses to re-engage you would move to have the borrower re-affirm the debt which essentially takes the discharged debt and re-obligates the borrower again.