How can one tell what to avoid? The essence of any system is never revealed except by time. [The cult that the Gra put into excommunication is a good example of that. However I think Reb Nachman was not included in that Cherem [excommunication] and if you look closely at the language of that document you will see why.]
This is the one and most essential issue of this age. For every age has some major issue. When kings ruled, politics was non existent. But with the Enlightenment the concept of a State began as an entity in and of itself and group politics began to take on a life of it own. Everyone had to be part of some "system" in order to be anyone at all. Then the age of cults began as an offshoot of that energy. Now the issue is how to get rid of the cults--i.e. what books to avoid and throw out.
My own path is mainly based on the Rambam which emphasizes four areas of study, the Oral Law (the two Talmuds), the Written Law (the Five Books of Moses), Physics, Metaphysics (by which the Rambam was referring to Aristotle set of books called the Metaphysics). [The Rambam was definitely not referring to any mystic type of learning nor any other book besides Aristotle because he said Physics and Metaphysics as teh ancient Greeks understood these subjects. Plus he had to be referring to Aristotle alone because there is in fact no such subject Metaphysics. Aristotle did not write down his lectures. That was left to his disciples. After they collected everything that they could about Physical sciences everything else they put into series of book they made up a name for "Everything after Physics"i.e. metaphysics] A Short Version of the Oral Law is the Rambam's own Mishne Torah. [The best way to do this learning is to go as fast as possible. Say the words and go on. By harping on every detail one usually loses the big picture. I saw a printed Mishne Torah with no commentary at all which is a good way to do it. But the second time around I recommend doing with with the כסף משנה ומגיד משנה, and as a separate session the Avi Ezri of Rav Shach. The book of Reb Chaim Soloveitchik on the Rambam is also great but I found it hard to understand. Rav Shach's is a lot more self explanatory. Perhaps today if I had another copy I might appropriate Reb Chaim more.]
But as I said, the main thing is what to avoid. And that is not everything outside of that list. After all we do have the Gra's emphasis on the "seven wisdoms" as the Trivium and Quadrivium were called during the Middle Ages. But most books of the religious world I find highly objectionable, and they seem to have a hidden agenda to destroy the Jewish family, and build up their cult in its place.
[The 1800's was the age of throwing out monarchs and making mass movements. Even the Musar movement and yeshiva movement were part of this process. Now the age of movements has come and gone. It is time to get back to personal responsibility and to learn Torah.]