Kabbalah as a religion would not be a heresy, that is like Judaism is a heresy. Kabbalah, as I understand it, is a practice of the Jewish religion.
For a heresy to be committed one must be a baptized member of the Church. I would say it is a heresy for a Catholic to get involved into Kabbalah as it goes against the Catholic Teachings of Scriptural interpretation.
Here we will run into a bit of trouble discussing Kabbalah. The trouble is that there is no central authority or unified teaching on the subject. The way that Kabbalah was presented to me was as the wisdom of Kabbalah. There were no rituals or practices. There was no Kabbalah prayers, or sacraments or even services. Furthermore, the Kabbalists say that their teachings are not a religion. I disagree.
I asked about things that I have read about Kabbalah. For instance I asked about Merkaba meditation. I was told that it is not part of genuine Kabbalah. I asked about prayer. The answer was that prayer was lifting your heart and mind to the creator, or Elohim. Prayer is only for the surrender of oneself. One does that in the manner that he finds best. Here is some more… God created man to receive His love. God is only love and His only action is bestowal. God can do nothing which is not for love. Man in both the broad sense, mankind, and also the narrow sense, one person, is originally capable only of receiving. As mankind, or Adam Ha Rashon, developed, just as an individual person develops from an infant, he begins to realize the benefit of bestowal. He becomes less interested in selfishness, and more interested in bestowal and love of the Creator. The entire point of Kabbalah is to enable a person to become more Godlike.
I read that an advanced Kabbalist can acquire anything that he wants. I asked about it. I was told that this is true. But - there is a catch. An advanced Kabbalist realizes that material things are an illusion. He only desires that which is spiritual. He can acquire all that is spiritual, if he has a desire.
I don’t think that studying these types of things constitutes a heresy. I did not follow through on studying Kabbalah. I found that the richness of Catholicism is more than adequate for my spiritual growth. You can probably tell that I found the subject interesting. To me, it is no more of a heresy than reading a book of Chinese proverbs. I really can’t recommend Kabbalah to anyone else, because I can’t recommend a school or teacher.
One of the things that I liked was the ability to discuss spiritual topics one on one with a wise man. This is a short coming for our Church. It is one of the reasons that we lose young people. If a young person gets involved in a cult, he will probably be taught directly by a high priest, coven leader, or other mucky-muck. These people are smart and they can be convincing. They know about Christianity. Our leaders know very little about them. When all we can tell a young person is, That’s bad, That’s dangerous. That is a sin. Etc. We are doing very little to divert their interest.
Notice the OP’s screen name, Young Thinker. His name describes the kind of person who is apt to be convinced to join a cult (No offense. You can’t help that you are young and thinking is good.)