Hi Khchan,
Here are my answers to your questions:
1) The notification letter does not list any required documents. It basically gives you your interview details.
2) Your friend will have to submit documents by 9:00am in the morning where he will only meet an embassy local staff - Not a consular officer. Your friend will then return at 1:30pm to meet with a consular officer. The local embassy staff asked me for the documents in the order they are stated on the "Diversity Visa Process" website in the following link:
http://travel.state.gov/content/vis...re-selected/prepare-supporting-documents.html
3) I was not asked for any additional documents other than those in the Diversity visa process list in the link I provided above.
4) Here's a sample of the 2nd notification letter:
http://forums.immigration.com/attachments/1901916_1497288330542621_8731982442197240434_n-jpg.237/
5) The whole interview lasted around 10 minutes. Questions were directed at me, my wife, and sometimes the both of us.
If your friend meets the requirements and has all documents in order, then he/she has nothing to worry about. DV process is pretty straight forward and the interview is the simplest part of all, provided the applicant meets the requirements and has everything in order.
Hope this helps.