my thoughts
I never take anything slower than 2.8 to any wedding. The 17-55 f2.8 IS is a wonderful lens and I think it's a must have for anyone using a crop body to shoot weddings with. Flash is critical also, even when shooting outside. A bride lit by the sun in a bright white gown will cause all manner of grief in terms of exposure without fill flash. Learn to use AV fill flash for outdoor. Indoor flash is often critical obviously. Look at a simple system like a "betterbounce" card (easily made yourself) to help diffuse on-camera flash. I use a Digital Camera Battery for fast flash recharge but failing that, be sure to have plenty of batteries. My second shooter has standing rules to shoot pre-ceremony with one set of batteries and then prior to the ceremony to change out the batteries for a new set, and then dump them out for a third set after the ceremony. I use 8gig cards but 2 or 4 gigs would suffice and not cause the problem that a bad 8gig might if it was corrupted. Change out cards before the ceremony if there is any question about capacity.
I think the ideal second lens is the 70-200 f2.8 IS. That's what I use. A simple 50 f1.4 is a great addition for speed when needed and very useful in low light particularly if flash is not allowed during the ceremony.
Be sure to have a backup camera and a backup flash. I do often bring a cheap zoom as a backup lens. Lens failure is relatively rare but dropping something can kill things.
A tripod is a must. Formals with a tripod will allow slower shutter speeds and more depth of field to ensure sharpness from front to back in a large group. Off camera flash ability from an STE2 or the canon cord is very, very helpful with groups and formals. Formals with on-board flash are a horrible thing.
Sounds like you plan to shoot raw and deliver jpg. Right on the money there. Shoot raw without question. I have Aperture and Lightroom and never use Aperture anymore.
Failing the 70-200 (forget the f4 version) I'd look at a 135 f2 or something similar.
People deride P mode, buy my second shooter uses it frequently, particularly when using flash, and while it's limiting in some ways, a solid 1/60 f4 will nearly always work reasonably well for indoor flash. Be very careful about shooting vertical with flash indoors. Shadows on walls from the side lit flash are really horrible. If there is no wall nearby you can get away with it if you must but I prefer to shoot horizontal nearly all the time and crop to vertical. Dunno if that's feasible with your camera but I'd bet so. 90% of wedding images are 8x10 or smaller and in the early days of digital I was tickled pink with 8x10's from 2mp cameras. Still have several such oldies on my walls. Your best loved images will all be about emotional content, not technical excellence, sharpness or noise-free qualities.
