Ok. So I was wrong about bonuses. I think it over 50 for bonus #1, over 200 for bonus #2, and I have no idea about #3 or higher, because simply getting a little over 300 points doesn't get you one.
I expected the different difficulties to have different levels, not just to have the same ones with fewer grenades. I don't like developers that make a perfectly fine game, but then try to make it flashier by making more of the same, and advertising it as something different. That just makes you lazy and deceitful, and makes me lose my respect for you, your game, and you ability.