Now I am currently working on efficiently rehabbing the property while they are living there.

Series LLCs and DSTS benefit from one state filing and one fee so they are cost efficient and streamlined.

Also, I'd replace that toilet with a modern, chair height, efficient model if it's not pretty new.

This is because the RE market is efficient.  

I have 7 Efficiencies, my Beach Home on a hill just back from the surf beach in Macae, Rio de Janeiro called Praia de Pecado or Sin Beach.

Yes, as noted unless doing a less common reverse exchange, where they'd buy your farmland first and then sell, the 1031 exchange buyer first must sell their investment property to become then become a 1031 buyer (with that 45 day time line to identify possible replacement properties starting).Other than researching owners of those selling investment property, think getting information to brokers would be most efficient (assuming they would be assisting their clients in selling and then locating a replacement property). 

He takes 1 trip to 1 house and gets paid twice (efficiency!!) 

I think I'm more interested in the BRRR, my main goals are to develop environmentally friendly, energy-efficient, and affordable houses.

The most cost efficient is to find something already built: a large house where you can rent out bedrooms, a multi unit where you can live in one and rent the others, a house with extra square footage that allows you to add a private entry and create a little studio or 1 bd unit to LTR or STR (?)

Everything on the market is wildly overpriced and as we all known would most likely need some sort of substantial repairs to get it back up and running efficiently.