Actually this is something I threw together for Winter Camps so I haven't taught the lesson yet. I just put it out there for anyone who wanted to use it, to take their own approach on it.
My students all know about the flag, maybe not everything, but they have difficulty describing it in English. My goal was that they would be able to do so after the lesson.
The Korean flag came up one day in class and the students couldn't tell me anything about the flag beside the colors in English, so my co-teacher and I thought it might make a good lesson.
I think the whole lesson, powerpoint, worksheet with questions and creating their own flag activity could be done in about 1 hour with an extra class. (Some students may take a while drawing their own flag) I do my winter camps in 1 hour classes then a break.
However the time line is very flexible, you don't have to do the worksheet, now its probably a 45 minute class.
As for how interactive, I would try to make it as interactive as possible. Before showing each slide on the powepoint, ask them a question first, example, what does the white background represent? and after showing the slide discuss everything on there. There is a lot of new vocab and between the class they should be able to discuss it with your direction.
I don't know if I answered all your questions, but like I said, this is something prepared for the future. I haven't sat down and planned the class minute by minute. So, feel free to use it in anyway that suits your style and class time.