This allows us to 1031 exchange post-sale into a new deal, compounding cash-on-cash returns and deferring capital gains.Let me know if you’d like to discuss further!

That will allow you to build the additional legal space further amplifying the value of the proprety (more HELOC money). 

There are lenders out there that will allow you to do a loan on something bought mid construction and is uninhabitable. 

Would a bank even allow us to mortgage multiple buildings on a single lot without it being subdivided?

Those failures are  more negligent than a PM allowing a guest who paid with expectation to stay at the house to remain there in the middle of winter when they arrived on a Friday evening as you described.For now you will have to rely upon insurance, I don't believe the PM acted unreasonably given the circumstances.

I'm guessing though that since the IRA owner isn't allowed to take out a salary, perhaps the SDIRA LLC will be required to hire employees? 

Somewhat unrelated, but I do not allow BiggerPockets to do business with partners who require their clients to sign agreements or otherwise agree to terms that prevent them from leaving what they feel to be honest reviews on BiggerPockets.

are you allowed to edit the chart of accounts? 

.- If you decide to have an LLC for each property, creating a Management LLC that all the other LLCs "hire" to run their books, will allow you to only require a bank accont for the Management LLC.2) You may not be able to do a Trust.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?