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

I would like to hear your thoughts and what I need to verify before making an official offer.

Trust but verify. 

Verifying last 2 years of rental history very important!

BTW I am a 10-99 contractor and have been focused on the rehab for the past several months, which affects my verifiable income.

., and ability to verify receipts and transactions (the verification is done by upper management to check and validate the revenues and expenses)4.

I dont get crazy with verifying past landlords or calling employers.

Assuming you meet real estate professional status (which it seems like you do - you'll just want to have a time log verifying) AND materially participate in your rentals, you simply wouldn't get that big of a year one benefit. 

Verifying last 2 years of rental history very important!

A good agent will vet a deal to some extent, but you will still have to underwrite it yourself to verify numbers.