Sprint - Questions

Hi All,

I've got several questions about Sprint.

1. Scrum Guide mentioned that Sprint is time-boxed at 1 month or less. I have a situation whereby at the end of the Sprint, the project left with some bugs. The Scrum Team and stakeholders agree that adding one more week can finish all the remaining issues.
what should I do in this case?
> Add the time-box to 1 more week
> End the Sprint still within 1 month and the next Sprint will be just 1 week
> any other suggestion?

2. When is usually Sprint length is decided?
> During Sprint Planning?
> Product Backlog Refinement?
> ?

3. When is new work (task) is added into the Sprint Backlog?
> anytime during the Sprint
> Daily Scrum

4. Do we have what we called 'Release Sprint' in Scrum? if yes, how many Release Sprint do we usually need?

5. Is the Items on the Product Backlog tend to be the same as in Sprint Backlog?
or just depends?
e.g. during Sprint Planning, we might found some item in Sprint larger that in Product Backlog.

Appreciate your advice.

Cheers.