Arma 3 has a great example of aiming deadzone. Go to 1:05. I'd suggest not giving people the options of turning this off. this way kills are purely skill based. obviously the crosshair would not be on.
As for the 4 levels of grenade throwing. I'd suggest level 1 is standard. press G for a quick grenade toss. level 2-4 would be pulling your grenade out and holding it your hand. when held (level2) its just like level 1 just a regular toss. if you mouse wheel down (level 3) your character would hold the grenade palm facing up for a short underhand toss. from level 2 is you mouse wheel up (level 4) he would hold the grenade palm down. In this mode you will do a running throw that goes much further then the Level 2 toss.