Might I advise you take up the harp? Wonderful to sing to, and very easy to get a beautiful sound from. Take up anything you like, but do it now & do it for yourself. Confidence is just something we all use to cover up the fact that we haven't got any, and musicianship is all about how well we make the inevitable mistakes. The vast majority of any audience is very much on your side and wants you to do well, and a 'folk' audience will generally respect you just for having a go - after all, you're the one that got up and did it, and they aren't.. Do it, and you'll inevitably get better at it.