We think we can get a large chunk of our money back as a down payment and then the 15 year note will be close to what we could rent it for.

Beating out large metro cities such as Los Angeles, New York, San Francisco, Houston, etc. 

For the mentor it is an opportunity to scale his business in a geographic region that he doesn't currently live in.  

They may not be large enough to handle large repairs, or even have the resources of people to call for this type of work.

An idea that occurred to me is the possibility of putting these 13 rentals into one bigloan and doing a cash out refi to cover a large part of the cost of our build, with the thought that the interest would then be deductible, which might have some tax benefits. 

they have their own equipment with a base station sensors cameras you have a choice to scale all starting at $300

After the Facts and Features section, there is a list of drop downs in large, bold font. 

Does it make sense to leverage our duplex to scale into a bigger multifamily?

No ability to scale.

I know too many people who have been taken by large upfront costs.