For example, SSN and validate it with a 3rd party background check company. 

If I can’t confirm 100% by sleuthing that way and talking to people, then I have the seller provide whatever proof they can that they really own the property, and also have my title company run an O&E, part of which is snail-mailing a letter to the owner in public record’s primary address so the owner gets notice that their property is for sale and hopefully call the title company and ask what’s going on if they’re not actually trying to sell. 

What would your mortgage company say if you could not pay because a tenant didn't pay rent? 

If one of the members of the LLC operate the company, its member managed.

I was looking at craigslist yesterday and noticed many pictures have a watermark over them with the name of the company posting the ad.

Properties go to auction Highest bidder wins 30 days later or so you get a tax deed.. depending on title company you may need to wait 1 to 5 years before they will insure title..

Can I get an independent umbrella policy through a different company?

From my own basic research it appears that many of the ADU companies have lenders they work with, but I don’t know that those would be the more creative or favorable terms out there.

We used the “homeboy remodeling company” and the house still is not completed (almost ~10 months).

There are companies out there offering low interest rates for 30 year fixed mortgages so you would not need to deploy all of your capital into one rental property and then play the waiting game for when interest rates drop.