Just like Minha, I'm currently living in Korea; but I'm Filipino-American, born and raised in the US.
I agree with Minha--when you get here, go to Insadong for all your traditional shopping needs. There's a lot to see and there are so many shops for souvenirs and goodies. You'll have plenty to choose from.
And since you're a tPF member, I'd assume you're gonna want to go shopping for some designer duds!
You definitely have to hit up Apgujeong for the luxury department stores, such as Shinsegae or The Galleria. These department stores (more like indoor malls) carry every designer imaginable!
But in regards to your second question, there are actually 2 InterContinental hotels: The InterContinental (near the underground COEX Shopping Mall), and The Grand InterContinental. My fiance and I have stayed at the Grand. Both hotels are really nice.
The women here always look very chic and put-together; so I think your best little black dress with some killer shoes and accessories will be perfect for the wedding, (maybe with some winter-weight tights)... because the climate will be
freezing in January, so also pack your best coat. The temperature will most likely be in the low 30's during the day, and the 20's and teens at night.
But you live in Chicago, so you know how to dress for the winter... (I'm from San Diego, so I get cold easily).
If you have any other questions, please let me know.. I'd be happy to help!