Much to my chagrin, adjusting difficulty in combat is a bit more obtuse than I would like. There are too many ways to alter the probabilities (change the number of dice, the target number for each die, the type of die rolled, or the minimum number of hits required) in addition to a few other factors that change the requirements (ie plus or minus DR). Furthermore, the ability to hit a target is not separate from the ability to damage a target in this system.
Rather than forcing a second step into combat (roll to hit, then for damage) difficulty in combat will now be based on adding or removing dice, though usually the latter. So for example, trying to shoot wile running removes to dice from the pool - obviously, its harder to keep rounds on target when you're moving relative to the target.
Hitting non resiting targets (ie can you shoot a paper silhouette on a firing range) isn't covered in the current rules. However, for the times when you need to do so, treat the combat attributes like any other attribute being tested and adjust difficulties accordingly. (Roll d6s against a set value.)
Sometime in the future, range may be changed so that the farther the target it, the higher the DR - since it gets harder to find that weak-spot and calculate a trajectory that strikes it.
However, I may also institute a range system not based on absolute distance between target and attacker as it stands now (as you note on page 20 using a pistol or rifle doesn't really mater for accuracy.)
Functionally, there will be range bands, and each weapon has a set effect based on barrel length. (Approximately: Pistols, SMGs/Shotguns, Rifles, Sniper Weapons, Missiles). Much like the DR/SDI system, a comparison between the weapons range and the targets distance will result in an adjustment of DR. There probably won't be a benefit for using weapons at extra close range, but this does represent the reduced kinetic energy of rounds as they travel.