I understand that if I rent this ADU out, then I can have a tax write off on the mortgage payment and insurance payment for the the ADU's sqft portion.

Also being able to write down/document goals I set earlier and see if they are being hit.

Also I am highly suspect of a company that would use an endorsement on their hope page of the controversial author Regina Jackson, whose claim to fame is hosting expensive workshops and writing books that claim all white people are racists. 

If you have anything in writing(texts, emails, contracts, etc) gather those.

Ideally, you want something in writing, but that is probably unlikely since no one will want to stand behind a not-yet-final number.

We have 9 rental properties and I have been doing taxes myself with Turbo Tax in the past, but wanting to make sure doing correct and then with this year working on mine own with LLC and being able to write things off (like mileage, LLC costs, Real estate license fees, etc), may be more than I want to deal with.

That someone will write a long answer that will tell you how to do it? 

All changes MUST be in writing.

One last question - is your assistant actually hand writing the envelop?

I also added one other habitat which I am very excited about, but have not started to implement yet...I would like to do it once a day, but I think I will start out with a once-a-week video journal entry!