Yes it’s correct... and also you can say “through so much trouble.”

It's fine, assuming you are upset at the time of writing or speaking. Your alternative is good too, although obviously its meaning is a little different, or at least more fully explained.

It is grammatically correct. It is what we call a mixed conditional. It expresses that if you prior knowledge that person would not you would be happier now. However, I would argue we would be more likely to say: I had known you weren't coming, I wouldn't have been so upset This is the third conditional and we use it to talk about situations in the past where we would change what happened.

Hello! I'm not an English teacher but I am a native speaker of the language. The sentence seems to be grammatically correct! As I'm sure you know, phrases and words in English can often be switched around and the sentence would still make sense. For example, saying, 'I wouldn't be upset if I had known you weren't coming' is also correct. I hope this helped you!

Yes, the sentence is correct! You can also write it as "I wouldn't be upset if I had known you weren't coming," which has better flow.