Heading to Korea for New Years - Anything I shouldn't miss?

Hi y'all!

I posted a couple of months ago about heading to Japan for a solo trip, and I got some good recommendations (including a great bar crawl that I loved). And now I'm heading to Korea for New Years!

I'll probably be doing a bunch of clothes shopping, anywhere I should head to? Especially for street/tech wear if possible, but I'm open go all fashion styles atm, getting tired of my closet!

I have a couple of the big spots, a palace and a temple for sure. I'll be in Seoul for 3 days, and Busan for 3 days (including New Years!)

Bonus question, if you know any tattoo artists around the area that you trust, I'm open to getting a new tattoo too!

Edit: I have a ton of Korean friends and one thing they mentioned was that Gangnam is overrated, I'll probably only go there for a couple of hours at most, unless there's something crazy that I'm missing.