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

I've worked with a lot of property managers and landlords on mold remediation projects and my experience has shown me the best time to find mold is when the property is completely vacant, and here's why.First, when you find mold you should verify that what is found is in fact mold.

The majority of that time is spent verifying rental income for the unit mix in the property.

Are there any other expenses that I should be accounting for or any way to verify that what I'm analyzing is a solid deal?

Make sure that you get the rentroll and the bank statement to verify that those tenants are paying that amount of rent.

It’s a proactive step that helps avoid costly surprises during construction and ensures that the ADU is designed with a full understanding of the site’s topographical nuances.A Building Verification Survey (BVS) verifies that the ADU is accurately placed on-site in relation to the property lines and in accordance with the approved plans.

LA is pretty friendly to allow those additional units but obviously you'd need to verify that specific area allows it depending on where you want to live.

Is it a really extensive change that they want to verify is possible? 

There are options for no-seasoning DSCR cash-out refinances, rates may be slightly higher and you may need to have two appraisals done to verify market value if it is significantly higher than 110k.

This feels naive. 2) Do I withhold payment until his insurance company will verify his statement about payout should he vanish?