“The Voice of Awe” – Halachic Debates on Chazanus and the Yamim Noraim

When does chazanus cross into tircha d’tzibburah?
Can a chazan use popular tunes, repeat words, or sing with a choir?
Should a professional chazan be hired for the Yamim Noraim, or is simplicity preferred?
Is chazanus an ideal form of avodas Hashem — or is it frowned upon?
What are the qualifications required of a Yamim Noraim chazan?