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I thought that the New Testament essentially "repealed and replaced" the Old Testament in terms of being the "guiding book for Christians"?
Only if you are a Marcionist heretic.
Every mainstream sect and even most of the odd sects consider the Law to still be valid. What they differ about is how to obtain Grace and who can receive it.