LLCs are very useful entities; I've also heard that they can be used for multi-person relationships as you say, for insurance, assets and other similar things. I've formed several LLCs (for business purposes) and can tell you it's pretty easy and quick as long as you know the rules of your state (or the state you want to form it in) and what you want to do with it. I'd be happy to share more if anyone is interested.
On the wedding, I second most everyone - do what you want! have the dress, the party the whole nine yards if that's what you want. But I would also just double check the exact wording of the bigamy/adultery laws in your state, just so you know exactly what the letter of the law is.