I have my first opportunity to take a private money loan from an acquaintance.  This will be a first for the potential lender as well.  I am still kicking around the idea, and I want to learn more about the concept first.  My first question is, how formal is a private money loan under these circumstances?  Is it as simple as receiving money from the acquaintance and repaying it according to the terms that we establish?  Can this be an agreement written between us, or is there any regulation involved?

You will want to protect the lender by having the loan show as a lien against the property. The name of the documents are slightly different depending on which state you live in, but basically you are creating a private mortgage and note.

Agree with @Amanda G. . If if would the your lender then i would need be at 1st lien position for subject property with loan amount of 60%-70% of the MAX ARV. Amount will be adjusted based on your experience and terms will be around 9%-12% with 1 or 2 points given my relationship with you. Lower your experience , lower the total loan amount. Lastly, you can have your Title Company to draft all docs prior to closing.