Can I use regular chili powder in place of Korean Chili Powder

Sure it should be fine. FYI I buy my spices at our local market- they have a section where they sell them by the pound. I like being able to go in for things I don't want a lot of and get just what I need. I've gone in before and bought just 2 star anise!

I think it depends if you're using a straight 'chili' powder, that is only ground chilis. Or if the "Chili Powder" includes a mixture of spices, like cumin, coriander and other spices (like the chili powder many use for chilis). I LOVE korean chili powder. I find the flavor superior to straight chili - with a mild to medium hotness and a sweetness. I use korean chili frequently whenever chili is called for and love it. I think it's worth the purchase if you use this ingredient often. But if you don't have it - it should be fine.

No, they taste different.

No, they taste different.