General Korea Advice

Hi everyone, I'm going to Korea for 10 days (staying in Seoul) and had a few questions:

- What are the best places to go shopping in Seoul considering I'm a teenager not looking for high designer brands but also looking for good fragrances? I'm from Australia where decent shirts can be $15-30, would you say stuff would be cheaper in Korea?
- What are the best restaurants/cafes places in Seoul and how much could a high quality meal cost? Also, how much does local street food/small shops sell food for generally?
- What's the nightlife like, any recommendations?
- How much should I expect to spend on food + travel (public transport) for 10 days?
- Where/how easy it it to get groceries (fruits, veggies, snacks)

Thanks.