You can do all these things using category settings and custom groups.
There are several topics that deal with these configurations, just use internal research
Basically you can create an “Audi Australia” group and you can configure the group so that users can enter only if approved by the owners of the group or only if users register with a particular email domain (e.g. audi.australia@your.site.com).
After that you need to create an “Audi Australia” category and you have to configure the permissions to “create see and reply” only for the “Audi Australia” group.
No one outside the group “Audi Australia” will see that category or see the topics that belong to that category (except for the staff of course).
All the categories with the “everyone can create reply and see” permissions will be public
No, users can’t create groups and categories. However, they can (usually) create PMs, and invite whoever they want to those, but they’re not “in a category” in the usual sense.
You also consider that the creation of automatic groups by users can be deleterious.
You could have dozens of groups dealing with the same theme that have a similar name.
Paradoxically, your users could create:
Audi Australia
Australia Audi
Audi Australia group
Australia Audi group
and so on…
before realizing that there is already an Audi Australia group. Or worse, a user could join the group, find users he does not like and create an Australia Audi group etc…
The simplest thing instead is:
create the Audi Australia group
make the group visible to everyone
configure the group so that users can enter and exit freely
giving “create see reply” permissions only to group Audi Australia in category Audi Australia
When an admin creates a chat channel, it must be associated with a category. The channel will then inherit the security settings of the category it is linked to, so if group X has access to category Y, then it will also have access to channel Y (either being added automatically or joining the channel manually, depending on the settings given to the channel).
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.