Mary Cooch (personal account)

Hello there. Please see https://moodle.org/plugins/registerplugin.php where you can register your plugin, making sure it meets all the criteria first.

"Descriptions" have been around for a long while in quizzes. Perhaps you created one a while ago, decided it didn't do what you wanted and so left it and made a different question type instead. People basically use descriptions for adding information or media (video,audio) at the start of the quiz that relate to all the following questions, or else they use descriptions a bit like labels on a Moodle page to divide up different areas of a very long quiz. Because they don't have responses or a grade attached to them they're not really question types as such but can  be useful. You can't automatically convert them to other question types; you'd have to copy the text or other content into the question type you wanted.

Do you mean users cannot create  accounts? If so then have a look at Email-based self-registration

Most phrases can be corrected within Moodle from Site administration>Language>Language customisation - see Language customization

Your guess is right, although just for the benefit of future readers of this thread, this is something which is possible with the improved Conditional activities in Moodle 2.7