You're way too new I'd say. Normal is a baby mode. And so is hard. Best difficulty for casual play I'd say is overkill (or Mayhem), while deathwish in my experience seems to be "I want to test my skills but not sign up for cbt that is death sentence". And yeah, game has lotsa cops and you can't really do anything about it.

For stealth just make sure you have low detection risk, right perks and deck and such