I would hate to refinance my duplex and lose the 4 percent interest on conventional loan.

Our financial support highlighted our commitment to providing the necessary resources for successful real estate investments.

My loans are locked for another 3-4 years at 4%, so I’m not interested in a refi.

@Jose ChavezAs mentioned notes are very standard documents that your attorney should draft.A PG is another separate document just like there also should be a loan agreement if to a LLC and some security instrumentWe use an attorney to always draft these and charge the costs to the borrower as part of the closing costs

It’s a worthwhile investment to safeguard both your assets and your financial future. 

I also have a mortgage (Solano Mortgage) company ready to go for when my tenant/buyers are ready to go get a loan.

That's the correct answer, commercial mortgages are a lot more flexible about down payment sources, etc, than home loans, but pragmatically (loan requirements aside) you need to bring SOMETHING to the table for anyone to want to bring what THEY have (down payment etc) to the table.

Are there any best practices for maintaining accurate financial records and documentation for these transactions?

Conventional loan How did you add value to the deal?

You can still get an FHA loan on those if you live in one unit as your primary.