I have sufficient trade lines as well but little cash on hand as funds are tied up in the deal due to unexpected rehab costs outside the rehab loan. 

I feel stupid asking, but is the template BP offers sufficient (I imagine it would be) or are there other templates for a contract agreement people would recommend?

If a borrower isn't willing to give you sufficient time to do your DD, that's a red flag- As Jay H mentioned, only lend to investors, NO owner occupants if you're not licensed- Ensure you know understand the deal and the exit strategies. 

However, it's important to carefully consider the rental market in the area where the duplex is located and make sure that rental income will be sufficient to cover your expenses.It may be helpful to consult with a financial advisor or real estate professional to get a better understanding of the risks and potential rewards involved.

On the same token, private money exist and you need to network a lot.

@Jay HinrichsRunning your investments as a business is essential- your point of having sufficient cash reserves, cash flow and being willing to make it through good and bad is crucial.  

But here's the thing with an FHA loan with either 3 or 4 units (duplexes are excluded from this), you must pass what is called a "Self Sufficiency Test."

@Stefan Demopoulos, as Jay said, the self-sufficiency test is the reason it wouldn't likely work in this interest rate environment.

I would keep it to two units as most 3-4 units right now don't pass a self sufficiency test and will require much more than 5% down.

Simple W9 should be sufficient