If there's one piece of advice I can give you, it's this: cakes are people too.
Your camera will be fine with the 18-55mm lens; you may decide later to get something a little longer and/or faster, but it's hardly necessary from the get-go. Wedding cakes tend not to be tiny, so the long end of the zoom range should give you a good "portrait" perspective on the cake. And it will let you focus closely enough to get the detail shots.
You will probably want to use a lens hood, since adequately lighting the cake for detail is going to involve off-camera flash (if you're not using ambient lighting or a continuous light source) and you'll want to avoid the possibility of any of the light striking the lens directly and causing flare. There's no need, though, for filters or any other lens-y accessories.
The 430e ii should be an adequate light source, but you won't want to use it "naked" -- the lighting will be too harsh, and you'll get overly dark shadows, especially in the fretwork-type details, flowers, etc., and behind the cake. Those tiny flash-mounted diffusers won't do a lot to fix that either; you'll want to use something fairly large. That can either be something to bounce the flash off of (like a large white reflector) or a shoot-through umbrella or diffuser panel. Or, if you're willing to spend a buck or two, a decent-sized softbox (Lastolite, Westcott and Photoflex, among others, make excellent units specifically for small flashes).
Going back to my lead sentence, the things that work for human brides will also work for their cakes. Well, except for direct flash -- you'll almost always want to light from an angle so you can see the details of the shape and texture. At the same time, though, you do want to control the contrast between the light and shadow side of things. You can use a reflector to fill, and later think about adding a second light at a lower power setting (if this gets addictive). I'd take it easy with the gold, though; the colour a standard gold reflector throws is really very yellow -- far too much for a white cake. There are reflectors with a silver/gold mix, sometimes in different ratios (Lastolite, for instance, has a "Sunfire" and a "Sunlite"). The difference between one of these "zebra" reflectors and a solid gold one is the difference between "white with vanilla shadows" and "white with caramel shadows".
If you start by treating your cakes as portrait subjects, you'll find that there's a lot of information out there to help you. Unlike a lot of food photography (which can be a real bear), you won't often have to worry about getting the sheen on sauces to look right, or conveying the feeling of heat or cold. You're working with the equivalent of complexion (the fondant) and fabrics (the decoration), so it's a matter of getting the colours and textures right as a whole. (Food photography as a genre can include some pretty intricate lighting to get all of the various disparate bits to all look right at the same time in the same picture.)
Avoid distracting backgrounds whenever you can. If you're shooting in your own space, you can use a seamless paper or vinyl background. On location, you may want to use a "pop-up" portable background (they're very similar to collapsible reflectors, and easy to schlep around, set up and put away) if there's a lot of unavoidable busy-ness.
Your camera will probably have an exposure setting for "high key" images (I don't know the Canon menus or settings), but you'll probably find that there will be a bit of trial-and-error involved in any case getting the exposure right. You'll want even the purest white to have enough body to it in order to have substance and texture, but not so dark that it doesn't register as "white" to the viewer's eye. That's a bit of a tricky balance, but if you keep to a fairly standard lighting setup, it won't take you long to zero in on a setting you can use as a fairly reliable starting point. It will only be when you're doing new custom colours that you'll have to do much fiddling around with exposure compensation and so on. It might help to use a grey card as a starting point.
Experiment a little. Play around. There's no reason why you shouldn't be able to take pictures that are at least as good as any of the ones currently on your site -- even those does by pros. You care about your cakes more than they do, and you know what you want to show to your customers.
