The problem for serious Christians comes with deciding how much of the Bible is literal, and how much metaphor and Parable etc.
Most sensible Christians agree that the Adam and Eve story is metaphorical, or a parable, but if so whence cometh Sin ? Perhaps Jan or someone could explain ? Certainly the concept of Sin as expounded by Paul and later N.T writers was not in early Judaism in that sort of form, so the whole concept is somewhat mired in doubt. And for a lot of the development of the Doctrine of Sin we have to wait until St Augustine of Hippo, and read what that old windbag has to say.
But Paul's saying Jesus was the Firstborn from the dead I do not see as a problem, or strange, within Paul's Christology.