How much should an architect cost me for a 1300sqft design?

No reason it should cost that much otherwise.

Because we are financing most of it, when there are repairs, how would you factor those costs into our son's ownership?

Anything you do remote will come at a cost of operational inefficiencies and a higher cost of doing business.

There was positive population growth, medium home price growth, low unemployment, good rent to home ratios, and low crime, all of which are factors when I start looking into an area to invest in.  

Cost efficiency while enhancing the design and functionality of the property What was the outcome?

Although I wouldn't suggest this and you don't need to do this, most lenders have a due on sale clause and this could be triggered (altough low probability) when transferring title out of a borrowers name. 

- Run your numbers (including all operating costs including property mgmt) based on current rents in AS IS condition and renovated.

It was mostly due to my day job income and low cost of living over a long period of time; however, real estate accounts for about 50% of our income through a small portfolio of short, mid, and long term rentals. 

Also, I found 2 ideologies regarding such development projects: Use one GC for the entire development or use that GC only for crucial trades such as foundation, framing, roofing , external siding, etc. and use sub contractors for finish and interior work to reduce cost.