If I'm paying cash to buy a property and have provided Proof of Funds, do I have to complete a Buyers Financial Info form?

I don't see why you'd have to do that.  However, I would strongly recommend that you retain an attorney to do a title search and title examination to ensure that you are receiving a clear title to the property and that there are no unpaid taxes, mortgages or other liens against the property.  Best is to deal with those before you pay, not after the fact.  My office handles residential closings regularly.  its money well-spent.