I need a plugin which let me configure tags needed per category.
So in some categories you dont have to insert tags,
in some other you should get an alert reminding you with a message to enter tags.
that Admin can to send meseege to all users and mention a group of all useres
I don't think that there is one. But you could make one yourself, of course.
You could have the same effect, I think, by just posting in the group, though. Once you want to get a public message to everyone on the forum, the forum is the best mechanism for that.