Live it in for a year and repeat the process, buy another duplex, hopefully with the same program if it still exists a year down the line.  

I believe from what I have learned about REI thus far, buy and hold real estate is the way to do that. 

And the real volume is conducted by wealthy investors who have the option to build marketing machines and flip, hold, or wholesale deal flow at scale.

We chose the one on one because were overwhelmed with everything that kept getting thrown at us ( business credit, Tax professionals, call flows, marketing ect) and I knew all I needed was for someone to hold my hand for the first deal. ( that's what the sell factor was during one of the weekend events, was that the one on one would stay until I signed our first deal).

Could you hold a 2, 3 or 4-plex in an LLC, live in one and still sell the entire building as a personal property sale after 24 months (no cap gains tax)?

There are many ways to use this based on your own financial situation but from the sounds of it, using this 140k HELOC on BRRRR's repeatedly can be a great way to grow your portfolio and can keep recycling the money. 

Buy and hold a turnkey SFH with 20-25% down.

Probably right, aiming for 1000 sqft livable space so not super tiny but still your point probably holds. 

@Mindy Jensen - I tracked down the dirty varmint, but there’s no need to murder him, as he died for his awful deed many years ago.Jean-Michel PapillonIn 1675, a Frenchman and engraver named Jean-Michel Papillon made the first repeating designs that matched on both sides.

You would structure the legal title such that each LLC holds a 50% undivided interest in the property as tenants-in-common.