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

This method is a little riskier and requires more work from the Property Manager. 

you can get financing witha  LLC but the lender will require a personal guarantee on the loan.

Instead of seeing this as an opportunity, people like you get offended, and their egos are hurt, so to defend it they will instead of accepting actual data, try to manufacture and manipulate the narrative to construct a realm where they could still be right regardless of where or not it is right.

What type of transaction fees should I be looking to pay and is there a down payment required?

They do, however, have up to 60 days to return a security deposit after a tenant moves out.If an eviction is necessary for nonpayment, landlords are required to send a seven-day written notice of the payment due.

I just learned this has now become a voluntary requirement for the time being as there is a court order to stop this reporting.

Most lenders typically require a 30% downpayment.

Windows would be my next check-point (less than R1) and then wall insulation: I would not be surprised if they have no insulation inside, but you can do blow-in, which only requires a small hole.A home looses heat in two ways: heat conduction (which you can slow down with insulation) and drafts, which in old houses is usually the biggest culprit.

Pretty much any regular bank / lender is going to require themselves to be in first position on all the properties... so I don't think a HELOC type solution is going to work across multiple properties with multiple lenders.