Getting points is not why I am here dear,
I will answer your questions from the Christian experience.
1. ) Satan rebelled against God because he was filled with prideful iniquity.
Being beautiful, He fell in love with himself & wanted to be worshipped as a God, not as a Creation of God, nor to be a servant of God.
2. ) In the Old Testament, humanity was under the Law handed down to Moses to the Israelites From God. The Law was never meant to offer Salvation.
We are Saved by God's Grace, not through our works.
The Law was good, but it did not redeem humanity.
The Israelites are God's adopted children.
They have the Lord's Glory, the pledges. Moses' Teachings, the true worship, & the promises.
The Law revealed sin.
The Law did not teach how to receive God's Approval, so those under the Law would try to set up their own way to get it, & they have not accepted God's Way for receiving His approval.
They were deeply devoted to God, but they were misguided.
God's Approval is based upon Faith.
Judgments by God were basically immediate during Biblical times, because humanity was not in God's Grace.
Not many had His approval, nor were there many walking in faith.
We cannot Save ourselves, that is one is attempting to do by just honoring the Law.
Humanity needed a Mediator, the Mediator IS Christ.
When Christ went to the Cross, He did it for all of humanity.
He took the penalty or curse that each of us deserve for breaking God's Law.
Satan must have known this, that the world would need a Savior, for he tried to destroy the lineage of Jesus the Christ on Earth, so he went after human ancestors...........
3. ) The Gospels were written by different people, ergo, variety.
4. OT Laws were not destroyed, but were fulfilled & changed by Christ's Crucifixion.
We now live by Grace.
To be Saved, we must believe in Christ, repent, & declare Jesus is our Lord.
By believing, you will receive God's approval, & by declaring your faith you are saved.
Clean / kosher food is under the Law, Christ cleansed our food through His Blood sacrifice on the cross, so it is now clean/ kosher to eat.
5. ) Despite their history, God called Moses & He also called Jacob, & many others.
Understand that God does not call the qualified dear; He qualifies the Called.
God is Holy. God is Righteous.
The Israelites / Jews were His chosen people.
Abraham's descendants Isaac over Ishmael, or Jacob over Esau was without regard to their works.
God has Sovereign choice to show mercy on whom He pleases & to withhold from others.
And, yes, like all of humanity do not deserve to be saved, for we all fall short of the Glory of God.
Yet, we are Saved by God's mercy called Grace.
Many times Israel had turned away from God.
God sent His Prophets.
God sent His Messenger angels.
God sent Judgments.
God allowed slavery.
God allowed persecution.
God, even divorced the nation of Israel once, then took them back.
Then, God Sent His Son Jesus the Christ for Redemption of all of humanity.
The Bible speak of Jews being in Heaven, in the Book of Revelation, 144,000 believer Jews / Israelites.
This can only happen because of God's love for humanity, for we all fall short of the Glory of God.
Believing in Christ Is our Grace dear.