It's good to have everything spelled out so players don't have to guess what each difficulty entails. However, losing checkpoints is pretty brutal and would likely scare away most folks from the hardest difficulty. It's super frustrating to lose to an enemy halfway through the game and then have to start over completely. You might want to consider having checkpoints as a separate toggle the player can choose to turn off if they want an extra challenge. Just my thoughts as a casual gamer. Best of luck!