I'd check with the host, but plan on arriving 15 minutes early to offer with last-minute set up (they won't let you do a thing, I'm sure) and to have a chance to visit briefly & thank the hosts. Your out-of-state family should arrive at the appointed party time like everyone else unless you check with the host first. Consider that the host will probably be running around doing last minute stuff and may not be ready for a lot of people to arrive early.
I'd bring a hostess gift as a thank-you, but only bring food if the host says it is o.k. They want to shower you with love and attention, and often that also comes in the form of food. (Unless, of course, you have special dietary needs or food allergies and know there won't be anything else for you to munch on. I.e. a milk allergy - bring a soy-based dip to share.)
I think it is awesome that your husband wants to do similar outfits! It may be hokey, but it sounds really sweet that he thought of it. Your family may love it.
Congratulations and have fun!