Keep in mind, however, that the IRA(or 401k if you ever get there) is investing in real estate on a standalone basis separate from you. 

Banks are giving me issues because it’s not rented and 3 separate lots on one sale.

Is there any reason I couldn't rent the bottom two units to two separate people?

Depending on billing, you might want to consider separate meters for each section if it is not already set up with multiple meters.On the metal frames, yes colder weather does not affect them as engineered systems are designed for specific locations, to account for snow loads, wind loads, etc.

But I lucked into this home with a permitted garage apartment conversion (separate entry, only shared space is the laundry room).

Try to separate the sales pitch from how they will actually run the business.

However there are lots of items we're allowed to separate out and give shorter lives to even without a cost seg.

Not an expert on this topic but the best success stories I've seen involved situations where the underlying business was done by a separate entity/experts who knew how to properly run the business. 

Besides tacitly giving the tenant the control by "confirming receipt" it also will require that I make a separate trip back to that property to inspect that particular unit on a date different than the others at the property I inspected on the planned day. 

They have the ability to manually separate business debt from personal debt if they choose to.There is the option of completely refinancing the note and putting it into the name of the LLC that way, but as it was mentioned in your initial post, and again throughout here, it’s not the best option because there are many regulations you have to abide by.