Queries

Hello All,

I have got few queries as below:

1. Who sets the sprint time-box and based on what factors for sprint 1 of a new project?
We know that the sprint length does not change. What if we realize in the 2nd sprint that the length of the sprint should have been something different to that is set.

2. Can we have more than 1 PO or SM for a project having multiple scrum teams working on same product backlog?

3. Can a PO also be the part of the dev team?

I think while I am going through multiple documents from various sources am getting confused :) .

Thanks,
Pragyan