nobody ceases to be Christian because they aren't in agreement with the next person on every verse in Scripture.
Exactly. There are core doctrines that one must believe to be a Christian and there are many other teachings that vary by interpretations and are not damning if a wrong interpretation is held. However, some wrong interpretations can erode into the core beliefs.
It also depends now much knowledge one has. A new Christian who never read the Bible will cling to some very basic beliefs until they learn more.
Stripped down I would say it is essential to know that Jesus is the God-Man sacrifice for our sins and that we are thereby declared righteous by faith in his sacrifice for our salvation.
I would add that by happy inconsistency, one may hold contradictory beliefs (thiestic evolution, and salvation by Jesus' sacrifice) and be saved, but with education one should see the inconsistency and make appropriate adjustments.