Trip to Seoul, South Korea tips/advice?

On December 17th 2012 to January 1st, I am planning on taking a trip to Seoul, South Korea for two weeks. I have been learning Korean, so I am not too worried about the language barrier. On the date I have set do you think it is a good time to go to Seoul? I only chose this date becasue I am on christmas break from December 24th to January 2nd. What is the weather like then? Do you have any advice how much extra money I should bring with me? Any tips or advice? Anything would be greatly appreciated!:)