They're good ideas, San San. I agree lots of your suggestion. Without Language topic (mục Ngoại Ngữ), everyone can use Vietnamese for your both thread and writing. And the language is not only English, but also Chinese, Russian...
But if you use English for them, you must write true English to other ones can learn English well. For example, you wrote "Hi you guys", San San. I know you is good English, but i think your first sentence is incorrect,maybe that because i never see it, so that repair "hi everyone" or "hi guys".