Look at Legal Notices under the classified section.

Now that I've got someone to screen, the landlord's process is to submit their rental application to a third-party screening service (applicant pays me the $30 fee to pass onto them), and if they're approved, the landlord informally OKs it without signing a lease or accepting rent payments from the new tenants.

That being said the obligatory caveat of me not being a legal professional and this not being sound legal advice from a reliable source needs to be typed.

Fannie Mae does not acknowledge the legal fiction that someone owning an LLC that owns a house does not own the house.

Unfortunately his plans have been approved and they've started some digging already.

Do not rely on it for legal advice.

What are the bare minimum requirements I should request in a written agreement/legal document with this individual to best protect my asset in case his investment fails or falls short.

What I like to do with my borrowers is to have them pre-approved and have financing already in place for them so that when they do find their property and are going under contract, everything is able to move very quickly. 

Do not rely on it for legal advice.

I really want to go ahead and get pre approved for an FHA loan in order to buy a house hack, but we are still working on saving capital and due to our budget limitations, I am fearful that in order to get approved we will have to wait until my wife has two years of income under her belt and both of us can be on the loan and we can do our first house hack.