Don't touch this unless you can afford to lose the entire loan. Recovery on a single, charged-off unsecured business loan will likely be less than 10 cents on the dollar. If you decide to entertain this, due diligence will involve digging deep into the business financials to understand cashflow, solvency, and liquidity, his personal finances, and searching for any liens or UCCs in place.
Given that he's got a long history in business but is struggling to cover $30k in Op-ex and marketing spend, my guess is that this is either not very well managed or is in distress. The fact that he expects $30k for 6 months on a 1.25-1.30 tells me that A) he's either borrowed in the MCA/alt funding/SME hard money space before or is aware of it and B) he's been turned down by the lenders he's already talked to. Coupled with the economic slowdown that's occurring, I'd be cautious to say the least. Borrowing this kind of money to fund aggressive spend on growth in a high gross margin industry is once thing; covering Op-ex shortfalls is indicative of near term distress.
For docs, at a minimum, you'll want a promissory note, PG, loan agreement, and a security agreement to attach to whatever collateral you can reach. You'll also need to file a UCC, although you'll most likely be stacked behind a blanket UCC from some bank.
Last thing - APR cap in NY was 65% last I checked. Check your math to make sure you're not violating this or your contract could be voided.