1. Members cannot delete a forum. The different forums and sub forums on TamaTalk are created by Admin and can only be deleted by Admin or Moderator.
I think maybe you're not talking about the main TamaTalk forums tho' so not sure what it is you want to delete?
2/3. If you start a group you can close it if you want. There's an option to "Manage Group"
Although be aware that any TamaTalk friends you have who are also members of your group might want to continue visiting the group and if you close it you will stop them being able to post and contribute to the group.
Generally, if you want a post or topic hidden from view you should report it and explain why / what the problem with the post is. Then a moderator will review your request and decide if it should be hidden. Hope that helps you out.