Is it possible to have various Sitecore instances/versions with the same installed Commerce Server?
I believe it can be done.
Below things need to take care:
- Change commerce databases (Shared and global) name
- Change commerce related indexes name (Commerce, catalog and customer)
- Change default port used for commerce roles
For more details please have a look below blog:
Hoping this will help you.
No, it's not possible.
Sitecore Commerce version must be compatible with
Sitecore version based on Sitecore Commerce compatibility tables:
https://kb.sitecore.net/articles/316437 - shows the Sitecore CMS/XP 8.2 and older versions compatibility with different versions of Sitecore Commerce and Sitecore Commerce Connect.
https://kb.sitecore.net/articles/804595 - for Sitecore XP 9.0 and Sitecore Experience Commerce 9 releases compatibility information.