The super ability is needed in itself. And you can't take it without the skills that lead to it.
I wrote about defense in the Knight thread, I'll briefly repeat that it's the second skill after magic power, and this should be used. If you don't like BDP, you can take Solid Defense.
Spellcasting is needed so that the hero moves more often and has more influence on the game as a result. I believe that the hero is the main strength of the Necropolis, and the troops are needed to last longer.
Attack is not needed. This is the weakest indicator for the Necropolis. You can take it only for Lucretia or if you only found Vampirism and don't have Subjugation.
BDP is needed for the Necropolis primarily at the start for the vampires. Replays have been posted where 4 vampires with BDP clear Utopia.