It depends how traditional or contemporary you want to be in the invitation. You could write, formally, "Mr. and Mrs. Bride's Parents and Mr. and Mrs. Groom's parents announce the marriage of their children, Cinderella and Prince Charming, on October fourth. A reception in their honor will be held on December 30th, etc."
There's nothing wrong with formality. But if you don't want to sound that formal, just relax it a bit. Above all, don't try to be "cute."
I think it will look and sound better on the announcement to announce the marriage first and then announce the party.
Where gifts are concerned, the question is *not* how much stuff they'll have to carry back with them (carry back where? Are they living in Hawaii?). That just comes along with gifts; don't burden your guests with guilt for it (I've seen this happen)! If the party is for only two dozen or so people, I wouldn't do the registry thing, but I would be ready to let invitees know, if they ask, what the couple would like.