Talk to a lender and see what fits your needs best. 

The 30 year fixed rate loan would be a better fit for this purpose.You might be able to think of some other scenarios but hopefully this concept is good enough to know the difference between the two. 

I'll explain to them that this is for BOTH of our interests and gives us an opportunity to get to know one another and make sure we're a good fit together. 

Then see if your strategy fits those.

Shoot me a PM with your email and phone number so I can add you to my list of Huntsville buyers if I get anything that fits what you’re looking for!

All that to say, you need to figure out what your risk tolerance is and how real estate can fit into that, not vice-versa. 

There are a lot of multi-family buildings on the street, but I don't know if mine will fit within the 12.5% cap.

Not sure if this fits this category but I’m curious to know how best to protect myself as an owner in a seller financing agreement if seller dies and heirs choose to do something else with property?

You either need to change your criteria to fit your market, or change your market to fit your criteria.  

I know a few "RE investors" from the Army that fit your Bro description perfectly.