Posted by: @minusmyx

How can I turn off Approve?

Please read this article: https://gvectors.com/how-to-disable-topics-and-posts-moderation/

Or delete the "You don't have permissions to see this page, please register or login for further information" message for New Topic and new users?

Don't follow you well. If you want to remove the message, just navigate to Dashboard > Forums > Phrases admin page, find the phrase, edit it and remove the value of the field (add the space instead of the text). 

If you can’t find some phrase you can add it using [Add new] button.

IMPORTANT: If you did some change in phrases, please don’t forget to delete phrase cache in Dashboard > Forums > Dashboard admin page.