The one piece of advice I would have given myself would be to vet the end buyer properly. 

Have this documentation prepared and recorded by proper counsel in your state to ensure the security of the investor's capital and that the terms of the note are in compliance with state usury laws.You or your entity will pay any points/fees, principal, and interest to the IRA based on the terms of the note.The IRA receives this passive income fully tax-sheltered.

It’s not a big deal just additional costs and paperwork to make sure everything is done legally and everyone is protected and have received and signed proper disclosure documents.

I was on the fence with that since I've had a friend who manages a property in Detroit distance without a proper manager, so he was able to be more profitable in this sense. 

If I understand you, you’re saying I’m not properly accounting the tax benefits (especially related to the depreciation)?

One thing to ensure is that it gets properly emptied prior to removal and that the fill valve is properly capped once removed. 

our second has come to us the night before with a concern though asking if we can "guarantee" the unit is "properly" cleaned with "appropriately strong products". 

Maybe you think it is, but once you run the numbers properly it's not an 11 cap.

If you don't use it properly, your LLC will probably be ignored by a court.

You could make the period shorter if you are confident that you can get a proper inspection executed in that time.