1. The fall in the Garden of Eden is completely irrelevant to Christian belief - it's not required under any circumstances (certainly not from a Protestant point of view?)
Its not irrelevent, it shows the nature of man, and gives a history of God's judgment in that we all have to die and have our sins forgiven to enter into God's kingdom. But with Christ, he conquered death with his resurrection, so that those who believe in him will find life, if they accept him as Lord and Saviour.
2. The sacrifice and Resurrection really weren't required and are just incidental - they are part of the story, not part of the meaning?
God requires a sacrifice. Man made sacrifice insincere and distorted the way. So the Saviour was born among us. Only the Son could please the Father with his living sacrifice and cleanse our sins. Only the resurrection could conquer death and reconcile us to God. This is God's rules, just like we cannot argue with him in making our lives end one day, we cannot argue with God and his need for a sacrifice. His creation, his ways, his rules.
3. Christianity would be just as relevant if there was no fall or sacrifice, and instead all that was required was for Jesus to appear and tell people He could forgive people their sins?