There is no constraint on the game mode you choose for this one, so it makes sense to do this on explorer difficulty. Beating the game first time around is going to be difficult as you are going to get stuck with some puzzles and other areas where there may be unexpected events. I would suggest you wait until you have completed the game on crushing difficulty before attempting this one. By then you should be good at the game and will also have solved all of the puzzles and any other road blocking events. You should know what to do and know the best strategies to clear enemies in a particular area.
This video guide should help you get through the game as quickly as possible and obtain the trophy. As you can see, it's possible to beat the game in under 5 hours using this strategy.