Buying second-hand PS4 games

Hi.
I would like to learn more about buying second-hand games for the PS 4.
1) If the game is single-coil, it is possible to take and not give? Just put the disc in the console and play?
2) And if the game is multiplayer, such as Battlefield 1? Is it possible to buy a CD with it and play multiplayer?
3) Sometimes, the game disc still has codes for all sorts of DLC. They get activated once on one account, and most likely the seller has already triggered it, right?