You've got a lot here. I'm gonna break it down a bit. First, Abraham did have some knowledge of God's commands and ordinances. How much, we have no idea.<quoted text>
Genesis 26:5 tells us Abraham had some knowledge before the Torah was given to Israel. The focal points for a Christian (disciple of Jesus) are:
1. He said the Sabbath was made for man - not Jews. Even in the OT is was to be kept by sojourners and servants in the land, and even by the animals. Even the land was to have a Sabbath rest every seven years.
2. That the Sabbath was set aside as separate by God at Creation.
As for one, I agree with your facts; but the "made for man-not Jews" is stretching the context. He was talking of His disciples plucking heads of grain, how it was "unlawful", and the main point is that the Pharisees had unnecessarily made the Sabbath a burden and a hindrance, instead of the rest and blessing it should have been. Nationalities are not at play here.
Two, God rested on the seventh day, hallowed it. But didn't reveal it to mankind until Sinai. To say any different goes against the text.