Lever throw is how much the lever moves in total.
Cable slack is how slack the cable is, ie. how much you have to pull before the brake pads start moving.
You'll need to adjust both together to get the brakes set up optimally. I would startPark Tool says:
Squeeze lever to test caliper brake. Adjust lever modulation setting by moving pads inward or outward from rotor by using both pad-adjusting knobs. To maintain the 2:1 ratio, turn the fixed pad-adjusting knob twice as many clicks as the moving pad-adjusting knob. For example, if a looser modulation is desired, turn the inner pad-adjusting knob counter-clockwise 4 clicks and the outer pad adjusting knob counterclockwise only 2 clicks.
The throw will be controlled by getting the cable tension righttotal gap between pads and then adjusting the feel with the 'outboard adjustment knob'disc. For a short throw, a small gap, pads screwed a long way in, for a longer throw pads further apart, pads screwed out.