Looking for Microsoft 365 best practices for a large dynamic company group

I’d keep two purpose-built groups.

Use a dynamic Microsoft 365 Group for SharePoint, Teams, files, the group mailbox, and calendar. Keep the Dynamic Distribution Group for company-wide email and meeting distribution. Microsoft treats these as different group types with different purposes.

For the Dynamic Distribution Group, you can enable Exchange moderation and allow specific senders to bypass approval. Mail flow rules can also help when approval needs to depend on the sender or message criteria.

Microsoft 365 Groups support moderation as well, but they do not combine every broadcast and meeting attendance requirement into one group object.

For meetings, marking someone as a Required attendee does not force them to accept, attend, or stop them from changing their response. There is no supported sender-side setting that makes attendance mandatory.

If attendance is mandatory, treat it as an organizational policy and use attendance reports or follow-up processes to track compliance.