are all the monsters from the movies on here. king kong?

Not all of the monsters appear in this game, but it has the second-largest roster of playable monsters in a game so far behind Godzilla Unleashed for the Wii (unless you count Godzilla: Trading Battle and Kaiju Collection). The monsters included are Heisei Godzilla, Burning Godzilla, Godzilla 2014, and Godzilla 2014, Anguirus, Rodan, Mothra Larva, Mothra Imago, King Ghidorah, Mechagodzilla 1974, Mechagodzilla 1975, Super Mechagodzilla, Kiryu, Biollante, Hedorah, Jet Jaguar, SpaceGodzilla, Destoroyah, Battra Larva, Battra Imago, Gigan, and Mecha-King Ghidorah. King Kong was actually considered for the game but didn't make it in because of rights issues.

When does the dlc code expire?

Which DLC Code? The Legendary Godzilla is actually free now on the PSN store if you have the PS4 game.

Will this be coming out on PC by any chance? Because that would be so awesome.

No, it doesn't make any sense for Sony to push this to PC. This game alone sells consoles for them. It never has and never will. Just like how Halo will never be on a Sony console.

Do i need to buy all the monsters or are they all in the game already

All monsters are in the game and can all be unlocked. The only exception to this is that you have to download 'Hollywood Godzilla' via playstation network, but it's free!