Hi Soyeon,
The first sentence is fine. Well done.
The second sentence. I'm not sure what you are trying to say.
"I don't think I'll (I will) be doing that for good." This would mean that you do not intend to continue doing that forever.
"I don't think I'd be good at that?" This would mean that you do not believe that you would be good at acting.
I hope this helps,
Stephen