Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
Yes, you can use Drupal fields in certain parts of Acquia Cohesion.
It depends on the use case. For fields and their field formatters use a 'Field' element, for data without field formatters, use a token.
No, the entity browser does not work for component defaults as the entities are content, not config.
Custom styles are CSS styles for classes.