1) 1.2 - In this scene of Hamlet, the King has his coronation and gives a speech to everyone. He has told everyone about his decision on why he has decided to marry so soon after his father's death. He says that it is to balance the mourning with the excitement of his marriage. The king married his brother's widow and the mother of Prince Hamlet. The King also sends Cornelius and Voltimand to Norway to give Fortinbra's Uncle a note basically saying "Tell your nephew to stop threatening to attack Denmark". Polonius allows Laertes to go to France. Hamlet asked to attend his old school in Wittenberg and Claudius says that he does not wish for Hamlet to do so. At the end of the scene, Marcellus and Horatio swore that they saw the dead King dressed in full armor, so they decided to tell Hamlet.
2) 1.2 - I feel like it is significant because without it we wouldn't know why the King did what he did and we wouldn't know that Fortinbra is planning on attacking Denmark. Without this scene the play would be very confusing and wouldn't have the background needed to make a clear statement.
3) 1.2 - Hamlet - Why did you want to go back to your old school? Fortinbra - Why were you planning on attacking Denmark? Question to anyone - when C/V were sent to Norway with the letter, what was the response since Fortinbra's uncle didn't know what was going on?