Headless server

Hi everyone,
I've read a bunch of docs about that, but things are really unclear for me right now concerning headless dedicated servers.
I'm making a hearthstone card style game with Unity and want an authoritative server which deals with all the logic part of the game for security reasons.
My questions are :
1/ Can PUN be used as headless server?
2/ Or is it better to use Photon Bolt for that ( or Photon Server ) ?
3/ Are authoritative servers executables have to be waiting for clients to come, or are they automatically launched once a room is filled with clients?

Thanks everyone.