Welcome Paul,
The first thing I am going to say is that you are going to love it. Ocean City, MD was also my first Nationals three years back. As far as your questions, here it goes.
Expect: As great time with fliers from all across the US. It is a week of pure enjoyment. You will get to meet so many different fliers that you will never be able to remember all the names and you won't have to
Dress: It is casual. However some people like to doll themselves up for the awards banquet. At least I do
Kites: I have always checked my kites in. I know that John Barresi has the scoop on that one. Something about sporting equipment, I know he will drop his two cents in at some point.
Anything else: Be ready for great times! Also the weather there can fool you, so pack for a little of everything. The last time we were there it was 90 degrees most of the week.
Hope to see you there.
Moon