In my opinion the term "structure" has no frame of reference in traditional witchcraft in any culture, including cultures like the U.S. where traditional witchcraft may be different for different people. Some find American ways, such as hoodoo or Appalachian folk magic. Some find foreign communities that they find a connection with, while others simply follow their heart. It is always about following your heart and walking a journey. Traditional witchcraft, by whatever culture it grew out of, is about that journey, not about building a structure like an engineer or architect. Some witches connect with certain paths, some are ancient and fragmented, some are living traditions that have evolved through time and cultural changes, some paths are just intuitive and from the heart. I think what is important is if as a witch the person in growing in knowledge, understanding, wisdom and has the skill to use all these things. To me witchcraft is about personal growth and results, to say the least.
I think I know what you mean when you say that you are looking for structure, but the idea of structure is dangerous to growth as a witch. Structure implies restriction and laws that may not understand the connection of things that are not structured as itself. The path flows like a river. It twists and turns, has deep points and shallow points, has points easy to cross and difficult to cross. Within the river there is life that may not be seen at first glance, but stay to look long enough and you will see the fish, the river rats, the birds, etc...Traditional witchcraft is like this, it can be unpredictable and also teaming with life and mysteries yet unknown to you. We never know everything, but if we are still enough, we begin to see more of the nature of the path.
Traditional witchcraft is also cultural. Since we have become more of a global community and have faster access to people and places, the craft evolves, just as we have as mankind. Some paths have more living history, but outside of closely knit cultures, especially tribal, such as in parts of Africa and Latin America, most witchcraft has evolved in some way, even those with a long history that have exchanged with other cultures. In my opinion Wicca has structure, traditional witchcraft has ways regardless of what culture a witch's traditional path may be based on. In modern developed societies we all follow paths that are different at least in some ways from those that started a path. This is because of cultural sharing. Whether someone is in an Afro-Caribbean, Mexican, or Celtic based witchcraft tradition, if you are not originally part of that culture, then there will always be some aspects that we must just follow our intuition and heart about. We can not completely connect because we are often not a part of the culture. There is no way to know the depths of the Celts, because we did not walk the journey with them. There is no way to completely connect with living cultures in witchcraft either. We can however journey into the unknown and become seekers. I have had foreign teachers, but I know that I do not know what it means to be Haitian or Mexican, so there is a part that I cannot ever connect with. However, that doesn't make the journey any less authentic as long as you can think outside the box.
I hope that gives you some of the guidance you are seeking. Throw away the search for structure and walk your journey. There are many good posts here, read them, they will answer many questions, and will create new questions too. Trust your heart, don't be afraid to fail or be wrong, the path is full of mysteries, embrace the mysteries. Even if you take a wrong turn, just knowing that is a sign that you have learned something. You can always change course, but no sailor has ever set out to chase the wind either.