Galatians 2 - Contending For Justification By Faith

Galatians 2 Discussion Questions
1) According to verses 3-10, how did Paul live the concept of justification by faith in front of the other Apostles?

2) In verses 11-14 Peter wouldn't confront those who still served the Law of Moses, yet Paul did confront. What would motivate Paul to deal with this issue, when even Peter didn't?

3) Why did Paul deal with Peter's sin in a very open or public way verses doing it privately?

4) In verse 18, why does Paul say that a Christian that goes back to keeping the Law has become a transgressor again?

5) If there's another way to be saved other than the cross of Christ, then why would God have put Jesus to the shame and torture of the cross?