I'd also like to split a unit and add a unit if it improves the ROI. 1.

Starting out, I would start with 2-4 units to get some experience under your belt.

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.

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

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

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.

There’s a whole different formula because they rent per person and it per unit.

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