Sound principles, good numbers and ability to drive to it make the most sense for me and allowed me to bounce back. 

(LLC) This is not a standard purchase and sale of real estate.Receive irrevocable stock power for the holding company.You are now legally the owner of the complex.

I was fortunate enough to start off with a 6 figure salary, so I have no debts, and am already investing in things like index funds, 401k, my company's stock plan, etc.

When one is purchased, it also comes with a share or stock of the corporation which is worth a certain amount.

Should I apply it to the principle of my primary residence?

Calculate the income produced by the property and subtract the expenses with the exception of debt service (Principle and Interest). 

I have looked at various investments, from the stock market to P2P leanding, to REIT's, etc...  

We also improved the house with custom closets, landscaping, curtain rods, additional cabinets, fencing the back yard...We also lived below our means so we could buy stocks.We participated in an employee discount stock purchase plan.  

(most of our Milwaukee housing stock is built in the 50s and many sewer lines have never been cleaned, so we do it as a precaution...)

@Kelly Bredlow, for me, I follow the same principle on any loan, regardless the size, or duration, regardless gap or HML or private lending.