What are the bare minimum documents you require from a business to provide to open an account/PPP Loan, and keep the bank in compliance?

If there is not a current policy or procedure.

I can't speak for PPP loans but for a deposit account I think the bare minimum would be collection of CIP elements so you're able to verify the identity of who you're doing business with.
And again, this is different depending on the type of business account. A dba would have different requirements than an LLC or a corporation, or a non profit etc.
Name, address, EIN Verification, formation documents (if applicable)….

But again that is the bare minimum, the FFIEC manual is the reference you want to use for higher risk accounts for ex: cash intensive businesses, NGO's, PSPs, etc.