How dangerous were these ideas that luther and the protestants were preaching

Dangerous enough. The Catholic Church didn't exactly appreciate things that Luther was saying. He questioned a serious source of income. But indulgences went far deeper.

They led Luther to proclaim 2 very important teachings as the central core of the protestant movement. The first was that Faith and Never works was the way to salvation. He saw the limitations of works and wanted faith to be the cornerstone of living a righteous life.

The second thing the protestant movement took up was that the Bible was the most important document in Christianity. This sounds like a given, but it really isn't. St. Augustine, for example and St. Jerome were held in high regard by the Catholic Church. Luther abandoned all of that by saying all a man needs is a faith in God and a direct communication with God to be righteous. [I'm interpreting a little here.] Righteous is not the word he would use. Whatever you call an individual, the centrality of the Bible let out confession.

Luther himself was not that adamant about his teachings in the beginning. He tried to distance himself from the reformation. In the beginning he was a mild scholar asking scholarly questions but in later life, he became a bit of an outrage. What made the reformation dangerous is that it divided religious thought.