If I am not holy, then I cannot keep the sabbath day properly at all.
"Remember the sabbath day, to keep it holy" Exodus 20:8 (KJV)
"Keep the sabbath day to sanctify it, as Yahuwah
thy Eloah hath commanded thee." Deut
5:12 (KJV)
Answer: There are several problems which your approach. First of all, you seem to assume that the word "holiness" means "moral perfection". In fact, "holiness" translates a Hebrew word that means "set apart for a special purpose". Your understanding of the word holiness is that it is the result of something that human beings do. In fact, it is the result of something that Yahuwah does. When Yahuwah adopts a human being as a child of His own and witnesses at at his baptism, that person becomes holy and pleasing to Him, regardless of anything that person does or accomplishes.
We would also question your assumption that Yahuwah gave requirements He knew people could not keep, and then formed the plan of saving them through the sacrifice of His son. We do not find the Bible to teach that at all. Rather, we find that Yahuwah made no unreasonable demands on humankind when they were created, but through their own choice, rather than any imperfection in either creation or divine law, Adam and Eve fell from grace. We agree that fallen man is no longer able to live by the law given to Adam and Eve. But the gift of grace in Yahushua is given in view of the fall of man, not in view of a law that was too high for Adam to keep in the first place.
It is completely irrelevant whether or not you listen to this website's warnings. It is also completely irrelevant of what you are "absolutely convinced." To you, the day does not matter at all. If that is so, it should be no sacrifice to you to keep it according to the commandment, just as you keep the commandments not to kill and not to commit adultery. The fact is that Yahuwah has said that the day matters to Him. That should be enough. All days are made by Yahuwah, and all days are alike. All women are made by Yahuwah, and all women are alike. Just because it doesn't matter to you what woman you sleep with, doesn't give you the right to commit adultery. By the same token, just because it doesn't matter to you what day you work on, doesn't give you the right to break the Sabbath. You do not earn salvation by keeping the Sabbath any more than you earn salvation by avoiding adultery. One commandment is as good as another.
A careful reading of lessons 9-13 in the Bible-study-lessons in the eCourse section will be helpful.