Well that is $1.75mm in equity just sitting there assuming it's all paid off with no additional liens.

In my experience as a contractor the trend is restoration of old homes with the addition of modern amenities is what more affluent people are wanting.

I have a couple unique and very cool situations, additional, so I want to make sure everything is aligned right regarding taxes with business structure. 

Ensure they have the experience to guide you appropriately and check references.In regards to the structure of the returns for the investor I would start with the return you would like to offer the investor and work backwards. 

The “house” is a double wide that has had additions added to it and sits on 10 acres.

Again, you may be able to get an additional 1% in credits if you can't have an agent.

If I just build a house that sort of looks like it could be multi family, such as, a house that is split into two, but doesn't have an additional range (still has an additional fridge and sink), would USDA be okay with this?

Additionally, they reinvest cash from the equity in their rentals into other rentals / vehicles in order to maximize their return and prevent "dead equity" from "diminishing" their ROI.  

If my property was fully paid off it would be an asset full of leverage to buy additional properties via refi.

Here's what my thinking is:Combining the loans in a new 15 year gives me 850/mo increased cash-flow (because they're all at different terms/rates)  YES, it creates a new 15 year loan, but it also frees up a property (#3 above) that I wanted to establish a LOC on to buy additional properties.