well from gear as u can see on my first item hotbar i have kept 5 item abi set/rahkir/lvl 24 robe of shadow/twilight/+8 int ring ...just reconfiguring the slots according with new system .. with that setup u +3 dc on all major schools necro,evoc,conju,enchant , major arcane lore from tod set+twilight, boost twilight with 120 combustion/elec,or glaciation/acid or watever combo u plz (i go fire/elec personaly xept situation like eeda that needed to respec on acid/ice) ,
The important bit is not to rely on your necro spells only ..circle ,drain,wail,fod ... because u gonna drain your sp like crazy and kill mobs slower ... so take draconic destiny twist in necro/faith/echoes ( my setup for most situations )
boost primary element spell power ,get energy burst+vortex ....and play with both nuke /necro spells ...u gonna rock the floor if u learn to combine em effectively ... like circle/mass hold fire burst !!!! dead !!!

or fire breath .. or burst and breath ...and can clean up if some1 survived with fod ...and so on that the idea anywho ^^