This plugin if Self hosted might help with some of the functionality your looking for.
Combined with groups and category security settings you can have topics in a category that are managed by the Op. Use groups to limit who can can create topics for discussion can le
- Audi Australia admin Create/reply/see
- Audi Australia members See/Reply
Members in the admin group could also be owners in the General group
In Category settings there is a setting to show a message if a person cannot post. So if Category has security setting
Everyone See
You can have a pop up message that has a link to apply to a group.