If you are not sure, review the daily scrum section in the scrum guide.

User Stories are not required in the Product Backlog as per the Scrum Guide. The Product Backlog is

a collection of all work to be done on the product, and it can include a variety of formats, such as

tasks, features, and technical requirements, not just user stories.

Product documentation can be part of a Done Increment if it adds value and meets the Definition of

Done. Scrum does not prescribe documentation but emphasizes delivering value to stakeholders.

It should be a working increment, but it's not mandatory to release it.

The sprint is the heartbeat of scrum, during the sprint the increment is created. The increment must

be usable and all the work that's part of the increment should adhere to the definition of done.

Best practices are based on past experiences and may not apply to complex, unpredictable

problems. Empirical approaches and experimentation are better suited to such challenges.

The scrum guide says: "The Scrum Team may also invite other people to attend Sprint Planning to

provide advice."

One product backlog per product

One product owner per product backlog, one product backlog per product

If you are not sure, please review the Scrum events section in the scrum guide