Get a qualified contractor to verify the cause and then make the necessary repairs.

I spoke with a sales rep from the Propstream team and they said that their sale price estimates (for non MLS users) are usually within 1% accuracy, but they didn't provide any way to verify that claim.

Verifying last 2 years of rental history very important!

My primary goal is to verify current employment, wages, and outlook (if they will go this far).

If you have a “Preapproval” it can be much more valid, the lender may or may not have gone thru the DU process  The reason to ask for a DU is to verify that the lender Actually looked at everything they should have in order to Preapprove you and that they actually Did the DU step  It is in Your best interest to provide the DU if you want the seller to be confident in your offer.

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

With the exception of a few states, transferring your property from your name to an LLC will not hide your identity, given your name will still be identified on the public record as a member of the LLC. 

Verify how the PMC manages your property and tenant(s).

Verifying last 2 years of rental history very important!

They are great for borrowers who cannot qualify for another option if they have no verifiable income, already have 10 financed properties, etc.