2nd PS4 setup questions

I managed to get a second PS4 for a good price, and I’ll be setting it up in the family room. I already have one set up in a downstairs bedroom. I have some ignorant questions about setting up and using this second unit.

  1. I assume I just use my same account username and PW on this; is my PS+ subscription good for this one also or do you have to purchase a separate PS+ account for each unit?

  2. Right now 99% of my PS4 gaming time is Witcher 3. I have a physical copy/CD. Will I need to move the CD back and forth between machines to play the game after I install it on the new machine? Also - if I purchase DLC on one machine for Witcher 3, will it automatically be installed on both games/machines?

  3. Whats the best way to share save-games between the two machines so I’m playing the same play through on both machines?

  4. What else should I know about running two PS4s that I’m too ignorant to ask? :)