I don't discount the possibility that the lender gets to finance 2 properties instead of just one but the proposition does make sense on paper and in theory. 

Duplex have different zoning that may permit additional units.

I've purchased legal assistance via MetLife, and I have requested my company HR to get additional legal assistance.

Those are both places you can get a lot of STR supplies from soaps through to furniture at trade discounts. 

Potential for additional rental income.Cons: Higher upfront costs for construction.

I don't think taking cash out in refinance raises your cost basis to calculate your taxable gains at sale unless you used the cash-out refi for an addition to the house. 

I have a good HVAC/plumber and an electrician (that I rarely have to use), in addition to a good carpet cleaner. 

I think NC is one of the few that negotiate due diligence money to seller in addition to earnest money deposit. 

Idenitfy properties with enough deferred maintenance for a discount and not enough for Full scale renovation.With 10+ unit properties, you can utilize more DSCR loans and drive the value through the income approach to valuation. 

In addition to numerous tradition RE related investments (most individually owned but some as LP), here are our unusual investments (both are RE related, but not what is common on this site)- I have mentioned this one a few times on BP, when fracking was just starting to be known to the general public (near turn of century), we purchased mineral rights in North Dakota.