There were Adam & Eve. They had 2 sons. They were the only people around. One son killed the other. Then he went to live in the Land of Nod, which was East of Eden. Which seemed to be a well-established settlement ~ where did it come from? ~ with a big population ~ who they? where they come from? And he married a wife from there. Who was she?

They had 2 sons. Correct. One son killed the other. Also correct. They had sisters. Cain married his sister. "And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters"
Adam and Eve didn't stop at two children. They had quite a number. And it wasn't against the law yet to marry one's sibling (God didn't forbid that until Moses came along). The gene pool was very strong, and would not have been harmed by intermarriage. The whole of the human population was and is descended from Adam and Eve.

And then, how about incest being forbidden? ~~ see e.g. Lev 18 vi ff ~~ ......Or is    the fact that that happened chronologically before [God] gave Moses all those rules supposed to make a difference?

Does the Bible say that it was a good thing that Lot's daughters committed incest? No. And plenty of evil came from that act. I don't condone sin, and neither does God. (Exodus 20:5)


In both Exodus & Deuteronomy there's the 10 Commandments which include 'Thou shalt not kill'

Please explain how this fits with your advocation of stoning to death which 'god' commands?

The Hebrew word in that verse is actually לא תרצח׃ ס, which literally translates as "Murder". Webster's 1828 Dictionary says this: "Murder: 1. The act of unlawfully killing a human being with premeditated malice, by a person of sound mind."
Murder is wrong in the sight of God. But capital punishment is not murder. "But if a man come presumptuously upon his neighbour, to slay him with guile; thou shalt take him from mine altar, that he may die." (Exodus 21:14) By killing another man, the criminal has forfeited his own life because he has taken the life of another. He has squandered the gift of life. Just as a man who steals from another man, Biblically the method of punishment is restitution (plus interest, depending). "An eye for an eye" (Exodus 2:24)
Is it more merciful to lock a murderer up in a cage for sixty years than to kill him as God commanded? No. Cages are for animals: NOT for humans created in the image of God.