I probably don't know what the hell I'm talking about, but wouldn't it be a better play to integrate (somehow) with a printing company? Or offer an export option that they can take to a local printer (as in the correct file format .eps, pantone color numbers, or what not).
Sorry if I am completely ignorant to the wedding invitations scene but I would think every girl deserves nice invitations and the convenience of a one-stop-online-shop.
Hmm maybe crowdsourced invitation designs.. ala threadless.com ?