Can topics be isolated to specific groups and not the full community? Furthermore, can members add topics to themselves (but ONLY select from pre-created topics)?

Hi there. This is a good question and I am not sure how we missed this question. Sorry for the later response. 

Recently, Tribe added an option to the admin panel that allows admins to choose if the regular users in the community are able to create a new tag while posting a content or not. You can learn more here22. 

Currently, there is no way to limit the usage of a topic for one specific group only.