The number of recipients of an email is limited, and the member addresses need to be disclosed to allow replying.
So, for this type and size of groups you will certainly have to use a mailinglist server.
Mailinglist groups can be convenient managed centrally, and allow to limit the control and user action confirmation to admins.
Deltachat however has no specific support for interacting with email from mailinglist servers yet.
How well it may work would have to be tested.