The 14 units currently rent for 675 with tenants carrying utilities.

This way you can judge what keywords are being eaten up by the bigger players and what keywords the competitors are not utilizing which goes back to getting an edge in the marketplace.

If you're able to double pay on the home you can build equity to the point where you're utilizing HELOCs to acquire investment properties which many investors do.

I would recommend checking out @Scott Carson material.  

My situation is unique in that my wife’s job gives us a place to live and they do not charge us rent or utilities.

I am not sure if it is something that contractors can estimate based on scope, material selection and others. 

I have been learning and researching about real estate investing for the last 2-3 years and have identified that I would like to utilize owner occupied multifamily units as my entry way into real estate investing.

Aside from the bulk discount pricing on material, savings on labor with dedicated professional, multi disciplined crews and the general passive nature of building safe investments and organic wealth is our rational and I am sure the rational of any established turn key provider.  

On the other, the lease they had prior to my purchase is much more like a residential lease than a commercial one, with me paying for a lot of maintenance and utilities that is not typical for commercial tenants.

Rather than paying it off quickly, you can utilize your extra monthly income to get more homes under contract.