Sorry, Nataly, you can ignore this. I thought you were asking about the English portion. Unfortunately, I don't speak Korean.
Since your question was whether these sounded natural, I'm giving you the way I think most Americans would express these ideas out loud. What you've written is correct, but some sentences are a bit stilted. Are you studying British English? In *spoken* English (at least in the U.S.), we would be more likely to say:
3. "Even when it's cold out, I have to take the bus to school." Use "out" rather than "outside."
4. Does "when the sky clears up" mean that it's raining? If so, I'd say "We'll go once it/the rain clears up. For now, let's wait inside." Definitely leave out "As."
5. "I have to go to the teacher's office to talk to him/her." "In order to" is less common in speech than in writing. Don't repeat "the teacher."
6. "I might go outside if I finish reading, but this book is pretty long, so you'll have to be patient." "However" is common in writing, or if someone is giving a lecture, but less commonly used in casual conversation.
Hope that was of some help. Best wishes with your studies!