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.
No. Helpers are coupled with the page once placed. Changes to the Helper layout will not affect existing instances.
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.
You don't. You apply a Descendant selector. These use a (Space).
Opacity is set using a decimal where 0 is transparent, 0.5 is 50% and 1 is solid.