1. Question: why did God tell Abram what was to come after he died. Was he supposed to pass this on? I know God's ways are not our ways, but what was the purpose of telling Abram about the Israelites. Was it for us to read now and believe... To see it came to pass as God said it would? Was this book written way before thee events happened with Moses?
1. Let's start at the end of that paragraph. It is Moses who recorded everything concerning Abraham by divine inspiration, even though Moses lived about 500 years after Abraham. So everything in Genesis is by divine revelation. And Abram would become Abraham because a part of this covenant would make him the "father of many nations".
2. What is recorded here is called the Abrahamic Covenant, and this covenant would be expanded and repeated to Abraham, Isaac, and Jacob. So Abraham was in fact expected to pass it on. It also overlaps with the Davidic Covenant made to David regarding his eternal throne on earth.
3. The Israelites (the 12 tribes of Israel from the 12 sons of Jacob/Israel) were a very significant part of the Abrahamic Covenant. So when you see "thy seed" in all the related passages, there are actually three entities who would be descendants of Abraham: (1) the twelve tribes of Israel for eternity, (2) Christ Himself as the seed through whom all the nations of the earth would be blessed, and (3) all believers in Christ who would be metaphorical and spiritual descendants of Abraham because of their faith.
4. Yes God wanted all Christians to read and believe what He said to Abraham, Isaac, and Jacob, since this covenant has an eternal impact. After the second coming of Christ, redeemed and restored Israel will be settled in Greater Israel stretching from the Nile to the Euphrates (as you have quoted). This has never been fulfilled.
5. Replacement Theology was introduced by the Catholic Church and adopted by the Protestant churches to falsely teach Christians that God was *through* with Israel, and these promises would apply allegorically to the Church. But since the eternal home of the Church is the New Jerusalem, we know that God has a plan and purpose for redeemed and restored Israel on earth after the Second Coming of Christ. Study Ezekiel and all the prophets in the OT.