You need to make sure that it's still a good deal to buy even when you don't live their any more.For example, if only $30 of your monthly rent pays toward the principal balance, it will take forever.  

No offense to your friend but I find it highly unlikely that he gets to keep the house free and clear for ever.

That's going to be tough for premiums as it takes a ton of factors into account.  

Lower unit does need appliances because there are none so I can maybe use that as a negotiating factor?  

Then focus on cash flow and other factors.

What factors you are considering to mark you rent at $1,300.

Repairs depend on a lot of factors, like the age of the building.My first duplex was 100 years old, and I had old galvanized pipes (that usually need to be replaced after 50 years). 

There are many other factors that you can pull into the software that Zillow provides for free (zillow.com/research/data/).  

These loans require a personal guarantee, so my credit and Debt to income are significant factors.

I know SO many military member that won't buy a house because they won't be there for ever, yet will pay a ton more in rent.