The worst part is the foundation.

Third parties must handle everything, and any profits from renting or selling the property must go back into the SDIRA.

Not saying they are bad deal but that one party always has the the win win scenario. 

It is a triplex so I don't anticipate it being a massive frat party type of issue.

If he agrees to let the other person move in, make sure you put that in writing and have it signed by all parties.

Use a 3rd party servicer in case the person still have some debt in the property to pay directly to the mortgage company.5.

In my case, I have residential rentals in one LLC, commercial properties in another, self storage in a third, and my real estate company operates in a fourth.

I think you will run into a related party issue rather than an LLC issue in regards to the 1031 exchange. 

A realtor that you are wanting needs to be new and fresh enough to the have energy and willpower to work their a#$ off, but also have some experience and education to bring to the party. 

In general, the major brokerages are somewhat greedy and they would prefer to keep both sides of the commission "in house", so before any new listing is posted to a site like LoopNet, Costar or Crexi, it is passed internally to every other broker in the office and then within the intranet for that company, to see if anyone has a party to do the deal with.