Each working group would have a user group associated to them, so Graphics would have a Graphic user group, Web Coding a web coding user group etc. A user group promotion would assign them to each user group (as a secondary user group) automatically.
If a user 'joins' the Graphic working group, then you would give the Graphics user group access to specific private forums. You would also enable 2 step verification for that user group. Similarly for Web Coding and the other groups.