A good guide to the history and various aspects of Daoism is
Eva Wong. Taoism: an essential guide
She's trained in the Complete reality school. The book has a good bibliography for finding texts on things like meditation.
I know that Daoism is a philosophy and Shenjiao a religion, but they go together and the best book about the religious side is probably
Jordan Paper. The Spirits are drunk.
He was a professor of both Sinology and Comparative religion, and converted to Shenjiao.