Damage types:

Guristas : 81% kin - 19% therm
EoM : 66% kin - 34% them
Angel : 56% explo - 28% Kin - 10% therm - 6% EM //Explo/Kin
Sansha : 60% em - 40% therm
Blood : 53% em - 47% therm
Drones : 50% explo - 18% kin - 16% therm - 16% em//EM
Serpentis : 62% therm - 38% kin
Caldari : 51% kin - 45% therm - 4% em
Gallente : 58% kin - 37% therm - 4% em - 1% explo
Minmatar : 45% em - 39% therm - 14% kin - 2% explo
Mercenaries : 54% therm - 31% kin - 9% EM - 7% explo
---------------------------------------
Main Damage type to shoot at the enemy:
Guristas - Kinetic
Serpentis - Thermal
Mordus - Thermal & Kinetic
Blood - EM & Thermal
Sansha - EM & Thermal
Angel - Explosive
Mercenary - Thermal
Caldari - Thermal, Kinetic
__________________________________________________-
stacking penalties?

1st - 100% effective
2nd 87% effective
3rd 57% effective
4th 28% effective