And if you feel the documentation is unclear on any of these points, please feel free to submit bugs.
We already did that once or twice, we'll keep doing it ;-)

They are dynamically detected on a periodic basis by the provisioner barclamp.
That would be really great, I tried that in one of my early attempts and it was not possible to change the repositories. I'm not sure, though, it could be due to incorrect network settings or something else I could have misconfigured.
I must have missed this part in the documentation:
Editing the repository setup can either be done with Zypper or YaST. Note that changing the repository setup on the Administration Server is optional.
Sorry for any misleading information.