Why is the preview in the Style builder not updating?
The style preview may not be updated because the refresh icon hasn't been toggled to the active state.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
Yes, this is possible by creating a custom element.
No site specific data is stored on the API.
The Youtube video embed is responsive so it should expand to the width of its parent. If you do need to set a width you can apply the Width CSS property through the Style Builder.