Hi Liesa,
A word of caution—I'm not sure what you mean by discovering a Chastain link through 23andme as I've never used 23andme. Be aware that if you have a DNA match with someone named Chastain, it doesn't mean that the Chastain line is how you are related. You could be related to any number of other lines in their family tree. So just make sure you know that the Chastain line is the DNA match, otherwise you're going to be chasing your tail for who knows how long.
If you do have Chastain ancestry, I'm quite confident you're actually descended from the Pierre Chastain who came to Virginia in 1700 -
http://www.pierrechastain.com/. Most Chastains are descended from this Chastain family. My Chastain line has a much smaller family tree and is unrelated to this one (Chastain meant chestnut in Old French and cropped up independently around many parts of France when surnames first arose i.e. having the same surname does not automatically mean a relationship exists).
Best of luck,
Joe