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

If sharing items is a must, your only option is to use an M365 Group. M365 Groups do support moderation, though the relevant settings are only configurable via PowerShell, see https://michev.info/blog/post/3546/did-you-know-microsoft-365-groups-now-support-moderation

For any additional "mail" features that you might be missing, consider "nesting" the M365 Group into a (non-dynamic) DG, where you will be able to configure such settings.

Oh, and do remember that Dynamic membership for M365 Groups is not free.