add the guard npcs sending players based on class to diff area.
Add spawns in those areas for the monsters
Make those monsters drop the appropriate tokens
Make an npc or a position calculation to see if the player has all the required items and that the devil isn't already spawned. If so, spawn the monsters
Make the monster drop the correct items.
Rather easy quest once you break it down into the base steps. Just focus on one at at time. You will need a monster spawn void, basic npcs, basic spawns and some drop rate calculations dependent on map/monsters