Opinion of the Bible's literalism/historic-truth/scientific-truth/perfection?

[Xeuma]

The idea the Bible presents a unified worldview is deeply flawed. We only need look at the two conflicting accounts of creation in the first two chapters to know that. That said, Scripture contains what God wished it to contain for the sake of our salvation through human hands. Fortunately for us, as the Catechism puts it:

Still, the Christian faith is not a "religion of the book." Christianity is the religion of the "Word" of God, a word which is "not a written and mute word, but the Word is incarnate and living". If the Scriptures are not to remain a dead letter, Christ, the eternal Word of the living God, must, through the Holy Spirit, "open [our] minds to understand the Scriptures."

Thus the fact I can't use the Bible as a history or science textbook is irrelevant.

[Xeuma]

Also, how important is the Hebrew part of the Bible to most Christians. Do you have to take any of it literally to be a Christian?

The Hebrew Bible is (more or less) literally half of the Christian Testament so I would say yes, probably.

I thought that the New Testament essencially "repealed and replaced" the Old Testament in terms of being the "guiding book for Christians"?

That's not a very good way of looking at things; at best its a very simplified way of how Christians understand it. If that were to be the case, why include the Old Testament at all? Rather, we understand a connection between the Old and New Testaments by typologies--that is, the New Testament is hidden within its predecessor waiting for Christ to make it known. (As a friend of mine (mostly jokingly) put it, the New Testament is the exact same as the Old, but much less exciting). Indeed, the readings of each Mass are selected with a view to these typologies. For example, the readings in Sirach about Wisdom are often read on Marian feast days.