"All of these people are depending on you" sounds the best

1 and 3 are fine for 2: I take full responsibility for what I've done (if it is past tense and already happened) I will take responsibility for what I will do (if it is future tense and you have not done it yet)

Clean Up My Room

I cleaned up my room,and Then, I found a hat. It was given to me at the countdown ceremony held in Times Square in 2017.
Almost one and a half years have passed since I visited New York. Time flew so fast!

If I have a chance, I'd like to visit New York again.

-----Your paragraph was good, but if you want it to sound more natural you can say this:

I was cleaning up my room and found a hat. It was given to me at the Times Square countdown ceremony in 2017.

It has been almost a year and a half (or you can say one and a half years)  since I've visited New York. Time flew so fast!

If I have the chance, I'd like to visit New York again. 

Why are you being like this? I never thought that you would change?

sentence A is fine but you could also say "let alone" instead of "much less"

"should have" would be better, but between those two options I would use "would have"

Do these two paragraphs make sense?

1. The only mistake I have made so far is that I have made no mistakes(or no mistakes?) even a single time. It backfired and has brought on more and more work to me as a result.

2. People in the office would hear him grandstanding toward the vendors, which was nasty to tolerate sometimes. One day, he was saying on the phone, "I'm not grandstanding, but I do have gotten offers from a few of the companies in this field. We may have met before - unless you had tried out in a different field."

---I'm not sure what grandstanding is. Is it the same as "boasting" or "showing off"? Those might be better words to use.

I would like to chat with you! I need to practice my Mandarin