Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
Yes. You should revision your Acquia Cohesion assets like other configuration using a service like Git.
Yes, you can use Drupal fields in certain parts of Acquia Cohesion.
Cohesion layout revisions are created at the same time as node revisions, but not always deleted at the same time.
Use the "Node Revision Delete" contributed module to manage your node and associated Cohesion layout revisions.
Use the tools included in the "Entity Reference Revisions" contributed module.
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.