Hello Gustave,
I am responding from the viewpoint that the Scriptures (in the original manuscripts) found in the 66 books of the Bible are God's word and are authoritative above all man-made theories and doctrines. I am not a Seventh-day Adventist.
I think you have laid out your position clearly, and your viewpoint seems to have the support of the Council of Trent, Justin Martyr, and Martin Luther. Yet I do not find your viewpoint convincing because many of your points are man-made theories and doctrines that lack support within the Scriptures.
The concept of categorizing God's instructions into categories called "natural law", "moral law", or "ceremonial law" would make sense to those who are content with man-made theories. But those categories are not described anywhere in the Bible. And those who teach such categories cannot agree regarding which category each passage of Scripture should be placed into, which shows rather clearly that it is not the Bible that specifies the categories, but that it is just a man-made system. Furthermore, the idea of using such categories in order to set aside some of God's instructions is not found in Scripture -- it is a man-made theory that has been superimposed on top of Scripture without God's permission and it directly opposes a substantial part of what God himself said in Scripture about his own instructions. In spite of the best of intentions, those who teach the categories of natural, moral, and ceremonial law also end up teaching things that are contrary to the word of God and contrary to the teachings of Jesus.
I plan to respond to specific parts of your post later, as I have time.