Why does the chazzan repeat the Amidah out loud after the silent prayer?
The chazzan's repetition was instituted for those who don't know the prayers. By listening and responding Amen to each blessing, they fulfill their obligation.
Question 2
Can an individual recite Kedushah when praying alone?
Kedushah is a communal declaration — "Holy, holy, holy" represents the entire community sanctifying God together. It requires a minyan; individuals skip it.
Question 3
What is the correct order — silent Amidah first or chazzan's repetition first?
The congregation prays the silent Amidah first. Then the chazzan repeats it aloud for those who couldn't pray alone.
Question 4
If someone knows only some of the Amidah's blessings, how do they fulfill the obligation?
The Rambam's practical solution: pray what you know, listen carefully to the rest during the chazzan's repetition, and say Amen to each blessing. You've fulfilled the full obligation.
Question 5
Can someone who sinned publicly lead the prayer?
The Rambam says: someone who sinned publicly (and is known for it) should ideally not lead prayer. But if no one else is available, they may lead.