*** Damage types to protect against ***
Angel's = Exp/Kin
Minmatar = Exp/Kin
Thukker Tribe = Exp/Kin
Blood Raider = Therm/EM
Ammatar = EM/Therm
Ammar navy = EM/Therm
Sansha's = EM/Therm
Mordu's legion = EM/Therm/Kin
Mercenary Commander = EM/Therm
Khanid Kingdom = EM/Therm
Mercenaries = Kin/Therm
Guristas = Kin/Therm
Serpentis = Therm/Kin
Rogue Drones = Therm/Kin/EM

Best Damage to NPCs
Guristas - Kin
Serpentis - Therm
Mordus - Therm & Kin
Blood - EM & Therm
Sansha - Therm
Angel - Exp
Mercenary - Therm

Stacking Penalities
1st mod: 100,000% effectiveness
2nd mod: 86,9119842% effectiveness
3rd mod: 57,1037996% effectiveness
4th mod: 28,2469117% effectiveness
5th mod: 10,5988834% effectiveness