Wedding Pack

I think a stuff pack would be the right size for something like this. The dresses and suits would be gorgeous, but also it'd be great if they had wedding clothing and jewellery etc. more geared towards various cultures as well (similar to what crocabaura said) since it'd be good to have a breadth of 'styles' you could have for your wedding, depending on the Sims you're playing, or the story you want to tell (if that makes sense). Also yes a variety of wedding cake would be amazing! more fancy ones and multi-tiered and such instead of just plopping a wedding topper on a single tiered plain white cake.

I don't know if such a thing exists in-game, I'm 99% sure it doesn't - but you know how you get the graduation photo after uni? It'd be cute to get a similar thing given to you of your Sims after they marry, like a cute romantic wedding photo of sorts. (I know we have the camera in-game, but I mean, a photo that isn't just a double selfie). Would be a sweet memory to put up in their house or something.