For 3), the math works like this: a high ROF / high kill# weapon generates the same average number of kills, but actually has a lower chance of scoring the first kill, which is usually the more important consideration unless you are fighting Fiends and RXS. That's not considering pinning (which only makes things worse).
For instance, a Deadbolt Launcher at short range using autofire with no other modifiers scores an average of 0.67 kills and has a 56% chance of scoring at lease one. For a Lance, not autofiring, the average of 0.67 kills is the same, but the chance of scoring at least one is only 52%. If the Lance autofires the average stays the same (using the upgraded roll rule any 6 becomes a 7 on a second roll of 4+) but the chance of scoring at least one drops to 50%. So fig for fig, the Lance has about 10% less firepower, unless you can spreadfire or attack Fiends to give your Lancers the chance of scoring multiple kills.
With a -1 modifier, the DBL has an average kill and kill chance of 0.33. For the Lance, the average is 0.33 but the kill chance is only 0.29 or 29%.
With a -2 modifier (or firing at longer ranges) it becomes more severe.
With using pinning, it gets really whacked. Assume a shot from 25" with no modifiers.
Normal fire: 16% to pin, 33% to kill
Autofire: 31% to pin, 31% to kill
Normal Fire: 29% to pin, 29% to kill
Autofire: 37% to pin, 20% to kill.
But any further penalties buggers it up because the system doesn't allow for a roll higher than 8.