Re: regarding spices…

They are often both called red pepper powder. The flakes are called coarse red pepper powder and the “powder” is called fine red pepper powder. The coarse gochugaru is used more in everyday cooking while the fine gochugaru is sometimes used in kimchi and making gochujang. More info on them here:

https://www.maangchi.com/ingredients/hot-pepper-powder

https://www.maangchi.com/ingredients/hot-pepper-flakes