The labor is lower, but that may also make it harder to treat your container as a "normal" shipping container on a boat - the window frames, door knobs, etc may stick out further than the regular wall of the container, which means they'd have to leave an empty slot on at least one side of your container. 

Granted, no risk no reward but this isn't a quarter slot machine in Tahoe.

The story: We are in the process of building a DADU and had a survey done.

This is not a slot-machine, it requires more skill and care than just sitting down, throwing a few $$$$'s into it and sitting back watching everything make $$$$.

Ideally a duplex on a 3.5% down FHA.Here in the PNW we see a lot of split-level homes that get converted into two units by adding a kitchen downstairs though I'm not sure that'd be enough space for you and your family.The ADU/DADU is a great place to look as well.

Finally, I have picked Househacking, MTRs, and ADU/DADU. 

I have confirmed with the county that an D/ADU is permitted on the property.

We can typically maximize older homes by finishing basement and converting it to an ADU, and build DADU in backyard if City, home layout and style allow that

My goals and strategy would take to to: build a DADU on an existing property for buy another multifamily property.

Lots of great AADU/DADU options if you're trying to exit upon completion.