Job request for blog mod

I want to be able to have blog categories that are created by the admin only. When members write a post, they will have to assign their post to one of these categories and not be able to create their own. However, they can still make their post private or public. But if they make it public, It will also  post to a community blog section under the chosen category.  pretty much exactly as it is done here in Unity. Need help making this work.

If you have questions please contact me.