None of the sites, including AirDNA which I like and use, are to be trusted at face value.

I'd recommend getting multiple quotes from service providers to see what pricing is going to look like per square footage.Without too much information provided and depending on the size of your home it could be anywhere from $5,000-$15,000+

However, the price fluctuates like stocks, so you may sell for more or less than your purchase price.REIT share prices can increase or decrease based on market demand, real estate trends, and the REIT’s performance.

Would this information being out there make it more likely for me to be linked to LLC and thus for anyone to try to "pierce it"?

But for the homeowner adding a single ADU, they likely have far better investment options.  

Also good points and this sounds like a good strategy to approach it.

On the flip side, you could purchase in lower-risk areas like Gwinnett, Cobb, and Fulton County and have a cosmetic rehab, but it'll come with a higher purchase price. 

I'm a current NARPM member with both the RMP and MPM designations, as well as a member of IREM, where I'm currently working on my CPM.

Anybody will charge you whatever you like if they know you're not familiar with crawl spaces, which is completely understandable. 

My mom would like me to assume the loan of her house to ensure it remains in my name.