Seller offering to hold a note on 3 duplexes

[ST King]

I have a potential deal in which a seller is selling three duplexes and is offering to "hold a note" for 20% down of the agreed upon purchase price, on a 5 year balloon at 10% interest.

First, I think "hold a note" means that this is a seller financed deal, right?  Or maybe they're just agreeing to finance the 20% down?  Can someone clarify what this means.

I've looked up that a 5 year balloon means the entirety of the loan will be due after that 5 year period is up.  So the mortgage looks like a normal loan for 5 years then "balloons" to the remainder balance becoming due once that period is over.  Is that right?

Assuming the properties are in good condition, in a desirable location, and cashflow well, how good a deal is this to start out my portfolio?

Any help is greatly appreciated.  Feel free to dumb it down for me, too.  I'm new here.

Thanks!