I have been to many Ayahuasca ceremonies. As you stated, it helps break down the ego mind's control. It is definitely important that there is a shaman, and the best is to hear through word of mouth of someone having a positive experience with a particular shaman. The shaman holds the space during the ceremony, much like how a yoga instructor holds the space for a yoga class - there is variation based on what that instructor brings experience wise, their own energy, etc.

Re: Ego - Ego is a tool, however it often gets stuck on acting as a coping mechanism. If ego's stuck on then it causes other problems of the body/brain/mind. It should act like subpersonalities, where there is a time to be a caretaker, a perfectionist, etc - however it becomes a problem if a subpersonality becomes dominant, like it becomes a problem if ego becomes dominant.

I have been going through a difficult journey, as was unknown to me beforehand, it turns out that my ego helped protect me and allow me to function by separating me from feeling/reacting to pain from a childhood injury. This disconnect from pain, improper perception of pain, allowed me to injure myself throughout the rest of my life - and then I was gradually exposed to it more and more, until a point where my ego no longer had enough control to allow me to cope through all of the pain.

I have had success healing some of the injuries with stem cell injections, however have run into incompetence that's built into our health-"care" system. I'll be posting about it longer at some point, soon I imagine. I struggle a lot daily.