There is also copper pipe on the gas supplies to the heater and a/c units which is not permissible. due to no accessible attic space, there is also no way to run electrical service to the closet to convert to an electric water heater.

The units without mortgages typically net $10-12k annually and the units with mortgages net about 1/2 that.

most of the construction loans out there will be for investment properties 1-4 units 

Your research on Oklahoma is actually reflective of 95% of the United States with regard to cash flow.  

This is a common approach for real estate investors.House Hacking: If you're open to living in one of the units, consider house hacking.

New $15k playground, pavilion, new water lines, and storage units.

Can I split the upstairs and downstairs to make two units?

I've had this happen with multiple units of apartment buildings.

Your CAP rate will be dangerously inaccurate if you calculate expenses incorrectly so let's break those down.Utility Set-up- As an overview you need to know the difference  between city-provided utilities and onsite such as Septic Tanks with Leech fields, lagoons, Wells, EtcGetting more specific what utilities are maintained by the community, paid by the community vs the tenants.I will give you a quick example, I own a park with a bunch of multifamily manufactured units of which I pay the electricity bill.

Also, just two days ago Fannie Mae made it possible to buy a 2-4 unit property as a primary residence with just 5% down.