If I change a Helper layout, will it change where it's used?
No. Helpers are coupled with the page once placed. Changes to the Helper layout will not affect existing instances.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
You don’t have to add units unless you want to use a specific unit or you’re adding Custom CSS properties.
No, the entity browser does not work for component defaults as the entities are content, not config.
Yes, this is possible by creating a custom element.