Using Microsoft Purview to limit OneDrive external sharing capability

I want to enable OneDrive external sharing, but only for a specified group. The members of this group may change from time to time. There isn't any way for me to do this in the SharePoint Admin centre - I can't limit this functionality down to a group, without also limiting it for SharePoint (not something I want to do). Therefore, I'm looking at suitable solutions using labels and Microsoft Purview.

High-level requirement: is it possible to have a label which is only available to certain users (based on a security group membership) in their OneDrive. When they apply this label, external sharing is made available to them?

Further details:

• The label should only be made available to users in a specific security group
• The label should only be made available to their OneDrive
• May be applied to non-M365 files in their OneDrive (e.g. PDFs)
• Once the label is applied, they then have the option to share the file externally
• The user is enforced to enter a link expiry date (maximum 14 days)
• Once a user has been removed from the security group, they can no longer use the label

Questions:

• Is this possible? Or even partly possible?
• If possible, what would be the recommended/best-practice approach?
• If the above approach is feasible, can this be applied to folders, so we share multiple files in one go?

I know I would need to enable OneDrive external sharing for all, but I'm trying to work out an approach to limit it to just a smaller audience. 

Thank you!