There are a few ways you can do this - more info here
MyMalcolm is the control panel of Malcolm! which you can access at https://my.malcolm.support/
You can delete your instances via MyMalcolm or ask the owner of any instances you are a member of to remove you.
Yes, the best way to do this is via an external host like YouTube or Vimeo.
Tags are a way of describing your content and allow an alternate way for your customers to browse FAQ's aside from search and categories.