If you're going to Vegas, you've got to have who ever is planning the party send out cool invitations! I found some AWESOME stuff on Invitations by Dawn. It has all sorts of funky Vegas-themed stuff.

Have your party whenever it works for you. Gettin_Hitched is right, you've got to do it when you have the time to enjoy it. The closer I get to my wedding date, the less free time I have!

Good luck!