Marbles,
The gist of the Christian Bible is that Jesus will return to usher in the kingdom of God. In the meantime, natural Israel was replaced by a spiritual Israel consisting of Gentiles and some individual descendants of the 12 tribes. The Israel’s ritualistic practices under the law and the covenant between God and the ancient Israelites consisting of the mitzvot was abolished upon the death of Jesus. Rabbinical Judaism adds nothing to Christianity: resurrecting the dead and healing humanity and being able to live for eternity. Christianity deals with proselytizing or preaching the kingdom of God and Christian living as outlined in the CS. The Oral law and the modern day Pharisaical approach concerns itself with the application of the Torah as interpreted by the Rabbis: ritualistic, ceremonial, tedious rules of conduct. Rabbinical law also enjoins 7 additional mitzvot —all for nothing according to the Christian Scriptures. There is very interesting information in the Talmud for example hiw the high priest had a rope tied around him before entering the most holy on the day of atonement, details about the celebration of booths and many other things but not important to understanding the OT from the perspective of the Christian Scriptures.
JW believe that blood transfusions violate God’s law. Best place to read about it is on the JW website. Can a Christian pump a quart of blood into his body for medical reasons as long as it bypasses his stomach? WT says no.
The Septuagint OT was available in the first century. First Christians were Jews who had the OT such as Paul who was a Pharisee. As Christianity spread so did the OT.