Where do I start with Reiki? Or crystal healing? Also learning herbs and essential oils...
In addition to what Mike has added, I would search for a diploma or degree in energy healing, as some metaphysical colleges provide this. I am a Reiki Master and Reiki is a very simple system , yet if you are studying healing in its truest form such as through a larger course, you will not only pick up key information a healer needs to know, but you will have case studies and a certain mount of hours to do which can also help a lot. For example, my diploma in energy healing that I did in Sydney was very advanced, so I learnt about so many things, such as counselling, anatomy, meridian lines, shamanic healing and ceremonies, intuitive healing, the auric layers, the earth star and transpersonal point energy centers, and so on. Where authentic Reiki teachings don't touch upon any of these things. I have also done a couple of crystal healing courses where I not only learnt about the crystals and crystal wands, but how to use layouts of specific crystals on the body to address specific health issues, as well as using pendulums as a tool during that process. You may find some great crystal healing courses to gain some kind of certification.
I look a Reiki has more of a formality, in the sense of having a qualification that people will know and respect, so they will come to you when you may actually be using an intuitive form of healing instead.
There really is only one way to heal, but there are a lot of healing forms that have been created which are really based on exactly the same thing. Once you understand the emotional link, which I discuss in a lot of detail in my long article
here, and also the chakra system (which I have a very detailed article about
here) in connection to that, then all that is left is addressing the emotional link with the client, and healing the issue through energy healing. So it doesn't matter what form you use, in the end those two aspects are what needs to occur. This is also how healing takes place through past life regression. Sometimes the emotional link doesn't need to be addressed, as the times are changing as the shift in consciousness continues on, so healing is going to change along with how we function in life.
You will be drawn to areas that you feel pulled to. So you mentioned herbs and essential oils, that will compliment any energy healing technique and modality you focus on. I think it's important to learn a range of modalities as that can not only help you find which one works best for you, but also provides options for people when you having a practice. A person will resonate with one option, but not another, even if you think one of those options is superior.
A very important resource to have is this book, which is one of the best for double checking the emotional link,
The Secret Language of Your Body, by Inna Segal. You will find that whatever you come across with clients will match up with what that book explains how the root cause, in one way or another.
Hands of Light by Barbara Ann Brennan is also one of those mandatory books to have read, and have handy.
What I have also found is that past life regression is really important to have as a skill set, as some issues can not be resolved just through energy healing. QHHT is really the most efficient and best method I have learnt, but LBL (Michael Newton) is also a good one. Some people require hypnosis based regression to go deep enough to reach the true cause behind the emotional link so that it can be acknowledged and let go, as well as healed.
The trick is becoming confident with what you do. You have to start somewhere, which will lead you on a journey to gaining that confidence and once you have it, along with the 'qualifications' that society expects of us as healers, then you will be on your way.