If its gonna be pretty much your first wedding, and can afford it, or if you know you can make good money off it, 24-70 2.8, and use your 100-400 when its about kissy time. Now if you cant dish out the extra cash for the 2.8, go with the 24-105 f/4, then get a 580 ex II(a must) that should hold you over rather well for dancing time, down the isle, group shots, pretty much all the basic need, depending how far you are, the 105 might cover the kissing part(i dont use flash during this time) depending how close you can get, without bothering the guests, remember this is her time, dont bug her, even thou its a friend or family, keep a good word of mouth for yourself. When its kissing time, you can get away with 1/30 if you can time it when they lock lips, they hold that for a second. But try to use that f/4 if you can. Remember it comes down to what you can afford to start with, and if you can make money off, because when your getting better wedding gear, you spending that extra money into more and better wedding gear, and so on, so that cost needs to be covered, to use it for you main hobby. Sence its a buddy, its good practice to see if you like it/enjoy it to keep going at it, and if you dont, just simply return the lens/flash or resell it for almost no lost of cost. Just look at some flash guides about flash bounce/fill to help cover quick thinkings.