I think the Tree of Knowledge is about having free will and choosing between what we need (God gives us what we need) and what we want (Satan/Devil/Evil gives us what we want).
This is how the evil in men triumphs over the good. Wants over needs.
There is much to comment on here but I will limit myself to one little thought from your long list of interesting, thought provoking ideas.
Christ is the lamb slain from before the world because He accepted His fate before the world was. He came here precisely to be slain as a sacrifice to cover our sin just as the scapegoat and sacrificial lamb were to take away or hide the sins of Israel in the time of Christ and earlier.
What the Israelites didn’t understand was that their sacrifices weren’t ever to take away their sins but were only to remind them that The Son Of God would come and would really take away their sins. They knew of The Messiah, they knew what He was coming for but the process ended up becoming more than it was supposed to, it became the end instead of the means.
Sacrifice was likely instituted in the early days of Adam, his sons offered sacrifice so they likely learned it from their father. Even as far back as Adam man knew that Christ would come to take away the sins of man.
The Lord Jesus Christ came here for that reason. As in Adam all men die so in Christ are all men made alive, as Paul would say. While Christ expects men to repent of their sins to be able to follow Him into Heaven and inherit with Him all His Father has, all men whether or not they repent and follow Christ will be resurrected because Christ loved us enough and unlocked death to let us all out of the chains of death.