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Comments like yours are insightful to me. Given the indoor and flash-less nature of a wedding, I can understand why fast glass is imperative. In your own work, what glass works best? In what situations? By lighting systems, I assume that you mean using a series of hot shoe flashes both on and off camera. Or do you mean more expensive strobes? Could you briefly elaborate why you feel these would matter more than focusing on a body. Thanks again Kent.
I know this wasn't directed at me, and while I'm not a pro in any respect I have a few comments to offer. (strictly speaking, you sound a lot like me - involved/interested in multiple fields and pulled into others). [Edit: This turned out a little long - apologies.]
I can't claim a lot of experience - I've been a GWC at a number of weddings, and been asked to shoot baptisms and other events for friends as the only photographer.
Weddings involve two different styles of photography - set/posed/group photos and the more "documentary"/candid stuff. During the more posed stuff, you have significant light challenges because you're virtually always shooting in crap light and you're expected to create very nice images. You need multiple flashes and a strong command of how to use/mange them because you generally are expected to do a lot on the fly and taking a minimum amount of time from the event. (on-location they'll almost aways be hotshoe flashes because strobes take too much time, room, power, etc. - you're on the run! They are back in your studio for the portrait sessions). Some of the set poses give you the choice to choose location and light, but those are only part of the body of work. During the documentary stuff, you're often in even worse light, which is where fast glass comes in. Your glass is going to account for more stops of light than your body, and the cool thing is you'll get it on your next body, too.
For example, you know how much the ISO performance improved on the D800 over the D700? 1/3 of a stop (though you do get over 2 stops of dynamic range). Even the king of low light (the D3s) is only a half-stop better in terms of measured ISO performance over the D700.
The specs don't fully represent the advantages of those bodies over the D700, but hopefully you get the point: Glass gives you a lot more than the body ever will, and keeps on giving. Get the "lower" body and better glass and you'll never regret it.
Which glass goes to style as much as anything, but I'd say you need a couple primes (a fairly wide one and a portrait prime e.g. 85 f/1.8) and a couple f/2.8 zooms (24-70, 70-200). For a lot of the set stuff, you'll find a good tripod/head system to be a big plus.
A comment or two on the wedding you're being asked to shoot: Are you the only photographer? If so, I'd recommend some reading and lots of planning. It is a BIG responsibility and damn hard. I've picked up a bunch of good information on shooting weddings/events (and photography in general) from Scott Kelby's "Digital Photography" series (4 books). If you're not the only one, and there is a paid pro involved, I'd highly recommend talking to that person. I always made a point to do that, and made sure to say they should feel free to let me know if I was in the way. I tried to limit my shooting to candids and other things that wouldn't impact his/her opportunity to make their money.
My personal journey has focused on getting a really solid kit of glass. I saw the glass improve the results from my D90 significantly. When it was time to upgrade, I went with a D300s over a D7000. Why the heck would I get essentially the same sensor over the latest sensor available (at the time)? Easy: Handling. The D300s is a revalation when it comes to getting the camera set like I want it very quickly and with minimal requirement to look at the camera itself. I love the switches and dials vs. holding a button and rotating while looking at a screen - which is the D90/D7000/D600 handling and even the D800 has some of that now (as noted above).
Net: Handling has saved more shots for me than a better sensor ever would. Glass has improved my photography more than any body could, and will keep paying me back on whatever I have next. Glass holds value very well, too...
I guess I can't call that my $0.02, can I? Probably at least a nickel...