1: it will trigger only on importing a raid, but will also count manually inserted raids
2: you dont need to activate null-sum, the player will get an adjustment (which can be deleted, manually) with the set up value (negative, but dont enter a negative number, would result in positive dkp).
3: it is always consecutive, so missing 2 raids, being one there and missing another one again, would not result in minus.
the "reset raid count" option: lets assume you have set the number of raids to 5, meaning when importing a raid, which is the fifth someone misses, he'll get minus.
you import the next raid, the player who received minus for not being there the fifth raid, misses again. if he'll get minus, depends on the "reset"-option now:
reset option set to yes: the player wont get minus for missing the sixth consecutive raid, he'll get minus for the 10th, 15th, and so on.
if you have deactivated "reset"-option, he'll receive minus for every raid he misses consecutively after his 5th raid, so minus for raids: 5, 6, 7, 8, ...
I hope this feature is working, not many used it till now, afaik. (But maybe it's just working fine, so i just didnt notice how many use it

)