I suggest that you find out what you are getting yourself into before doing something as advanced as a wedding.
Flashes are the least of your concern. Your ability to deliver quality photographs in a challenging environment with the RIGHT equipment should be your main concern.
Before accepting or rejecting your friend's offer, do a google for wedding forums, take at least a week and find out what is involved to do a proper wedding as a photographer.
You may find that what you deliver, compared to even a mildly experienced professional will not do the couple justice. This is a once in a lifetime event that can never be duplicated, it would not be fair to them to potentially deprive them of capturing this event properly.
I never really knew what it took to do a wedding well... until I shadowed a professional wedding photographer three times and learned the basics (yes, doing it 3 times sure as heck doesn't qualify me to do even ONE by myself yet, and I consider myself a fast study).
The duplication of HIGH quality equipment is an important factor. As an example, the photographers that I shadowed, each carried around $5000 around their necks, and had 2 backups of everything that they considered more critical (batteries, flashes, cameras, light stands and so on).
A few examples of what the pro that I shadowed did that normally a "friend" doesn't consider to even think about during a wedding:
- He had a checklist of over 200 items to do BEFORE taking the first shot
- He had another checklist of 50-250 shots that he ABSOLUTELY had to get, and this list came from one or more conversations with the couple
- He told me that on average, he lost 5-7 pounds on the day of the wedding, from running around. I believe him, as I lost 3-4 pounds myself and I often took breaks that he never took.
- Forget about socializing, eating with the guests, dancing or even taking long pee-breaks. If you do, you potentially can lose that once in a lifetime shot that will NEVER happen again.
- Can you get in to take pictures of the bride dressing or getting ready for the biggest day of her life? If you are male and a friend of the family, not likely... but a pro does, and thats one of the most poignant parts of the day for the bride!
- What happens if your flash burns out? What happens if your camera breaks? How many batteries does it take for you to take 500 shots? 1000 shots? 2000 shots? The photographer I shadowed took an average of 2500 shots per day, and I added 1500 to that without trying very hard.
- Being honest... how good are your post processing skills? How good are your photography skills? Can you operate a camera in aperture or manual mode without thinking about it, just doing it? If not, you have a longer way to go than you just imagined.
- On camera flash? Only a true beginner would dream to use a flash on camera at such an event. On camera flash results in flat lifeless boring and lower quality pictures than if off camera lighting is used, and even then, it would not be all that often. You cannot use the flash during the most important moments of the wedding (like possibly the entire ceremony if in a church). You will not use flash if you want the best quality shot (most of the time!) in conditions where ambient light can offer superior results, if you understand how to exploit it.
- Tripods? Monopods possibly? Always needed in low light conditions.
- How about lenses? No kit lens will ever work to give you a useable picture if you are at the back of a church and the ceremony is candle lit. Fast lenses are a must (F/2.8 and numerically lower are not options... they are mandatory). Most professionals have a range of 3 lenses for wedding use: wide angle, medium and zooms in the 70-200mm range. None slower than F/2.8 as a rule and more often when the demand is there, F/1.8 or F/1.4 are used to get the shot.
Ok, ok... Time out!
I am NOT trying to discourage you, but I am trying to make your realize the enormity of the responsability and challenges required to do a wedding. And if you are already thinking "wow, this is a lot"... I've not even touched on the all the more important aspects and also other 95% of what is needed to do it right.
Seriously, do your homework, find out what is involved and make an educated decision... not an emotional one, or one based on false pride or a pressured one. Formals and portraits are just a TINY aspect of a wedding!
Good luck.