At least I found an answer to my third question:
How to programatically add user and password information for certain (Smalltalkhub) repositories.
(MCRepositoryGroup default repositories
select: [:each | (each isKindOf: MCHttpRepository)
and: [each locationWithTrailingSlash includesSubstring: 'http://smalltalkhub.com/mc/MyName/']])
do: [:each | each user: 'MyName'; password: 'MyPassword'].
The credit goes to "Pharo: Tips and Tricks" by Mariano Martinez Peck