I will just pick out one portion of your question and answer it. THe symbolism of Kantorek is pretty straight forward and to me, also particularly relevant given the overall message and theme of the book as an anti-war novel.
His name itself is likely derived from that of a "cantor" or the person chiefly responsible for leading the singing in a church service, particularly a Catholic one. Kantorek leads the chants of the boys, to an extent, prior to the war as he tries to instill in them the image of war as glorious and a place where boys become men, etc. He leaves out the horror and the ragged madness of the battlefield, largely because he's had no real experience himself.
This is emphasized again when he is shown as a particularly ineffective soldier.