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

Even one 4-star review can significantly impact your score when you're just starting out.Keep in mind...pricing & photos are the two most important things to guests as they book - make sure you have them right from the start.

There are so many versions out there promising the same thing I just don’t know which one to to with.........

I'd agree with @Devin Peterson, best way to get this answered is to get a few quotes from different lenders and compare - either on BP Find a Lender or just googling (also if you post a version of this in the Classifieds subforum - or it might get moved there, you can interact directly with DSCR Lenders here - although this subforum is more about technical questions).

As long as you mom can qualify on her own (with her credit score), I don't think adding you to the loan application would hurt even though your score is not good (but I would still double check that).

If you stay at 60% or below of your homes, you can get into the 5s pretty easily with a point or two, even with credit scores as low as 680. 

The interest rates on these loans from the programs are usually at a much higher rate as they do not qualify people based upon a credit score.  

Now that that's in place you'll want to start building credit through that LLC so you have enough credit time & a quality score to qualify for a property using your LLC.

What's the lowest credit score you will allow?

We came across a company called Seek Capital because, unlike other companies, they are willing to approve setting us up with lines of credit based on my wife's credit score and do not require a high monthly revenue like other companies.