Regarding Genesis 6:1-4, I think every scholar would agree that nothing is obvious here, and we should be very tentative. I just gave one reading here. There are others.
Not really. Read here: What is the Image of God?
Okay, then perhaps slow down a bit on Genesis 6:1-4. It seems that you are just hearing about the “human” vs. adam distinction.
Several views. Heiser and @jongarvey would say the Divine Court.
Remember also that the name of God is different in Genesis 1 (Elohim) and Genesis 2 (Yaweh Elohim).
Sure, why not? Maybe in means the “lineage of Adam”? That is how many people are taking it. Adam seems to be an important word here, and it might be used with some precision through out Genesis.