@Julie McCoy I would be at my parents farm on the weekends anyways, but this would shave an hour of my drive each way to work and about 100 miles total off my vehicle each day. 

I have thought about investing in notes but this seems like an investment vehicle with many more moving parts than owning RE. 

I'm wondering if they would be able to transfer the 500k into a self-directed 401k and pay for the construction of the home through this vehicle instead of having to pay cash for a downpayment.

I have the opportunity to acquire a vehicle at an incredible discount.

That block seemed in decent shape, though, and I didn't see any overt signs that would have made me sweat about leaving my vehicle parked out front. 

There are number of other tax professionals here on BP who might help including @Michael Plaks and @Nicholas Aiola.Regarding your IRA LLC questions you should have a professional on your team who is well versed with this vehicle. 

I have a more precise excel spreadsheet set up with a much greater analysis but the numbers I provided were estimated from that to just give the basics (may not add up exactly due to rounding). 

I would rather make the highest cash flows possible and I thought 4-plexes would be the investment vehicle to get me there: Would I still be better off starting with single or duplex considering what I have just told you?

If you have cash or equity it should be moved to a different investment vehicle not simply allowed to wallow in a property where it is essentially being sent to die.

I plan on using 4-plexes as my vehicle to get there.