You are all correct except the second sentence. It says 오늘은 김치를 만들어요. This means that a dude named "Today" is making kimchi. So long story short, the word 오늘 is a subject in this sentence so you need to change it wouldn't be. Such as:
오늘은 김치를 만드는 날이에요 = Today is a day where (we) make kimchi.
오늘 김치를 만들거에요 = (We are) going to make kimchi today.