With these, I'd almost say yes, however which one depends on when the person is leaving. If the person was about the walk out the door saying "I'm leaving now" I'd then say " I wish you weren't leaving". If the person said "I'm leaving soon, I's then say "I wish you wouldn't leave". I hope this helps, but i'm sure somebody else can explain in more detail for you ^^

I'd say these are pretty much the same. The first would be used more in the present tense, then the later would be use more in the past tense. Example: There are a lot of people in the park today. There was lots of people at the park today.

These are all fine, but remember to add the noun/subject. One in five "people" prefer to stay at home. Four out of five people prefer to stay at home

Sloth 

For this I think while is used because the parcel is travelling. So its like "If your parcel is damaged during transit" or "while in transit". The "during/While" is there to say that it's going from A to B. I find that "while" is used because of the time its in transit. Describes the sense of time. Sorry if this isn't helpful, but i'd say the difference is only slight.

A letter for a neighbour

Dear Bob.

First of all, I am sorry to disturb you to about the loud noise from my house. My house started renovation last week and  will finish at the end of this month. I understand that you work at night time and you usually rest during the day, because of this I promise you two things until construction finishes.

Firstly, we will not make any noise from morning to noon. I had the carpenters  work without any machinery which are the causes of any noise. Secondly, I am going to have additional soundproof sheets put in to surround my house. Now they're only thin sheets and I do not think those are enough to keep the sound out. I am going to request for them to be made three times thicker than now. I am going to do this as early as possible but if you have still any complaints, please let me know. I am always a reasonable person as you know.

Your sincerely.
Tom