You've also got fundamental differences in the nature of God - Trinitarian (God is Father, Son and Holy Spirit) and non-Trinitarian (God is God, Jesus isn't God, the Holy Spirit isn't God) - which then means Baptism/Christening/Dedication is either in the name of 1/3 or just God.
Whether Holy Communion can be taken by unbaptised people (Open or Closed).
Whether Communion can be taken by infants, children or only adults.
Whether Saints have the ability to intercede or not, whether they're actually saints in the first place. Whether they existed, are metaphors or are minions of The Devil.
Whether there has to be a leader who is the only way for a person to access salvation/knowledge, the nature of that leader.
Whether there are particular books in the Bible or not.
How those books should be interpreted.
What should be done at death or other life stages.
How to behave in terms of food that is eaten, observing a day of rest, what language is used in worship or outside, what prayers are said and the words they contain, how to dress, how to act, roles of women, men and children, what to have in the home, what medical treatment, what family planning, sexual behaviour...
And differences in Eschatology - what happens at Death - whether Christ is going to return for a thousand years to rule Earth, whether he isn't, whether there's a really shit period just before or if He's only going to come when everybody's a believer. (Millenarianism, Amillenarianism, Historic Premillenarianism & Dispensationalism) - whether a literal Antichrist is going to show up, whether the souls are in Limbo or Purgatory...
Whether there should be music, whether people can be possessed by the Holy Spirit on a wet Sunday morning in a disused pub, whether churches should be lovingly constructed and made beautiful (or if the disused pub is fine because the Church is The People, not the building), whether people can guarantee their afterlife just by being a member (or are instantly doomed for not being of that particular flavour) or if they have to do anything...
Whether the Bishop of Rome is a top bloke, an allied equal to their top bishop (but perhaps somewhat mistaken) or Satan himself, whether everybody was made in the image of God or just Men (or just white men), if women can be religious leaders or simple breeders.
In short, anything that you might have learned at school or seen on TV about Christianity, there will be hundreds of other Churches that completely reject it in favour of the complete opposite - and will have been the cause of violence, murders and great suffering on the part of others, sometimes outside that particular church/denomination/sect and within.
You could spend ten lifetimes studying (not aware of any that believe in reincarnation, but there's definitely a possibility somebody does) and still only have scratched the surface.