Just cash your checks.As for an up charge due to the additional occupants; charging additional rent for his girlfriend & child would fall under familial discrimination.

We were actually wanting to buy a duplex with it this second time around but the bank was telling us that we’d need 20% down on each additional unit being we wouldn’t be living in it.

We would likely have to add additional egress point for the upper unit via a deck and some stairs. 

How does one build their portfolio to a level where you can quit or work part time without causing a significant reduction in the money coming in?

(Did you have a contractor look at the building[s]) Are you taking out an additional loan for that? 

Test the math of your plans with a few years of price reductions and/or stagnant inflation and see how it works and if you'd be OK.  

In addition partner with a Realtor for sales and rental comps and become familiar with the U.S.

You could enter additional Holding costs in the Misc block.  

List of items to be done - (inspection next weekend)HVACAir Conditioner addition to current forced air furnaceElectricalGarage door motor to 1 car garage door Install recessed lights in living room, and new light fixtures in bedrooms, living rooms, kitchenReplace light switches/outlets to square plastic whiteFlooringRemove carpet, tack boards one main floor and top floorInstall vinyl plank flooring throughout main floor Same baseboardPaintingPaint all wood trim whitePaint kitchen cabinets whitePaint all wallsStructuralRemove half of kitchen wallSliding door for half bath on main floorKitchenReplace kitchen counter top, and match bathroom vanities with sameReplace kitchen sinkReplace appliances with stainless steelBathrooms Replace countertops with same kitchen counter materialGeneral workInstall window blinds on all windows

There are a number of purchase/sale/holding costs to look out for, that I compiled into this post here: https://www.biggerpockets.com/blogs/8814/70530-fix-and-flip-project-costs-purchase-sale-and-holdingI see that you're located in South Dakota, so in addition to those costs you'll also need to contend with the Contractor's Excise Tax, which is a 2% tax imposed on "prime" contractors engaged in "realty improvement projects" in South Dakota.