On is correct in this case.

You should only use "they" when talking about people and "that" when talking about objects. Although people ignore this rule a lot anyways.

Either is correct but the second is a more normal way of saying it. The first is about who you are as a person, whereas the second is about people that are similar to you. I have heard the first used in books more often, but the second in actual conversation.

It really is just poetic language, in a normal conversation people wouldn't speak that like. Unuttered and unspoken mean the same thing. If I were to say the same thing but in normal words I'd say, unspoken words, or, the words that were not spoken. The reason to say unuttered words unspoken is to add extra to the sentence. It adds flavor and flair. I would be surprised to hear the sentence outside of a poem or a theatrical play.

The second sounds better, but I would also say movie theater instead of cinema. While cinema is the right word, an average speaker wouldn't use it.

A needle is the more commonly used form of syringe. Average speakers would say needle, but medical professionals will say syringe. An injection is the act of putting a substance into someone with a syringe.