Hello, 1) Seems incorrect. This looks like a dependent clause (Subject + Verb, but not a complete thought), so you need to more to make it a complete thought. - 'Look how many students there are in the class room!" or "How many students there are in the classroom does not matter." 2) Correct/Not awkward 3) Same as #1 4) Correct/Not awkward, but I wouldn't say commonly used. 5) Incorrect, it is just not how we say that. 6) Correct/Not awkward. This is actually an example of how to fix #1/3.

Hi. Here are my corrections to your questions. 1. How many students there are in the classroom! (This is incorrect because you are asking a question. It would be correct to use an exclamation point if you were to say something like: I love my students! 2. How many students are there in the classroom? CORRECT. 3. How great a person he is! (Incorrect.) It would be better to say: He is a great person! 4. What great people they are! CORRECT 5. How great people they are! (Incorrect.) It would be better to say: They are great people! 6. I want to know how many students there are in the classroom. CORRECT