Outfit for a wedding in America

[TeamSledward]

I've been invited to my cousin's wedding in America.
I've been invited to the Rehearsal Dinner on the Friday evening, and then the wedding ceremony is at 5.30 on Saturday, followed by cocktails, dinner and dancing.
Then there is a Sunday breakfast reception (coffee, juice and light snacks, apparently...)

WTF do I wear?!
I have a lovely flattering black lace dress that I would like to wear to the wedding, but I have concerns. I wouldn't wear black to a British wedding, but is that acceptable in the US (especially with a cocktail party after)?
And what about the Sunday do? Any weddings I've been to here, where we've stayed over, everyone just rocks up to breakfast in the hotel bleary eyed and wearing their jeans.

I'm 5'2, and a larger lady. Big boobs, apple shaped, but cracking legs (even if I do say so myself!). Size 16 waist, with an 18/20/22 top, depending on which shop I go in.
And on a budget too! Don't really want to spend more than £75 on a dress, would love to spend less that £150 on outfits for all three occasions.

Sorry for dropping this - have been busy with RL.

You will definitely need a car, public transport that far outside DC is practically non existent, you would be totally stuck.

There are some nice shopping areas near Leesburg, and Leesburg also has a great outlet mall with quite a few good shops.

Americans may not get wasted at weddings - although they did at the most recent one I went to - but beware of drinks. I always need to ask for extra tonic for my gin or I would get something that is close to 50-50, which would floor me in no time.