I'm a amateur photographer (but have had paying gigs at concerts and music video shoots) and I've told 2 friends absolutely NO when they have asked me to be the main photographer at their wedding to "save money." This is their special day, and I don't want friction to occur if I missed "the shot" they were looking for, or heaven forbid photos come out blurry. It is too important, and as your friend you should be there to share the day, not stressing over being "the photographer". The point of wedding photography is to have a lasting memory and record of the happy day. Both you and your friend will regret it if things don't work out. I would not recommend you being the primary photographer, if you want to take photos great! But with your level of skill and experience doing weddings, advise them to hire a professional.
From the questions you ask and you stating this is a new camera for you, if you still want to do your friend's wedding photography you need to read the manual and take photography classes to get up to speed. The wedding day will be really stressful just in trying to capture the spontaneous moments and coral people for group shots, let alone trying to work a new camera with varied lighting conditions to make sure the photos aren't blurry, dark, washed out due to the flash, grainy, etc.
If you want some basic information these tips would be a good starting point:
http://www.lifepics.com/Photography-Tips/using-manual-mode.htm
http://www.lifepics.com/Photography-Tips/low-light-photography.htm
http://www.digital-photography-school.com/?s=wedding&search=Search
http://www.digital-photography-school.com/weddings-5-ways-you-can-be-a-working-guest
http://www.digital-photography-school.com/50-must-have-wedding-photography-shots
Think really hard about what your friends wedding means to you and what your participation in the wedding means to them. Are you wanting the wedding experience or a stressful job? Are they wanting a friend to share the day, or are they wanting an employee to get a job done?