Swift or Objective-C for native iOS development and how to learn it?

1. In 2016 should you use Swift or Objective-C? What other languages you can use for iOS?
2. What are popular libraries, frameworks for iOS development?
3. Is it required to use Xcode or which IDEs you can use?
4. What are main principles of building, positioning and styling UI on iOS? Should you use XCode's drag'n'drop? Can you use HTML and CSS?
5. What video tutorials, authors, articles would you recommend to learn iOS development (professional level, no need to explain software engineering and programming basics)

Qustion is not about JS and hybrid development.