After quick research it appears 10 is the answer as I found someone with 12 posts and they are not listed as a new participant. Also starting with 100 it will list an approx. number of posts next to you. I found someone else listed as new participant again with less than 10 posts who has been a member 9 years. So if you never posts more than 10 times you will always be a new participant.
Shopping Western NY, Northeast and Central PA, and parts of Ohio and West Virginia. Have car will travel anywhere if the monies right.