mfing with a necro might not be the most efficient because effective mf has diminishing returns and thats further compounded by the necros slow killing speed. but whatever suits you, for the most part you want to find runes and those arnt affected by mf.
I disagree that necro is really slow at mfing. I find it very fast. All you need is 3 thing: Enigma, max CE, beef up your merc(Infinity, Fort, Vampgaze or helm that has LL+ DR%.. your set to mf fast. If you have resist problem, could add some resist small charms. Now you have allot spots to add up MF%. Shako, mf shield, war trav, chancie, goldwrap, rings, ammy, Gheeds and still can kill fast. All you need merc to kill 1 then its all over to this group.
Personally, I would take HOTO over those because you will be using corspe explosion more than anything else. For +3 and resistance, FCR. You just need your merc to kill 1 mob then its all over for this group.
Max block due to teleporting.
Move points in mages to bone wall(bone armor) so you can absorb more damage. Max CE, put 5-10 points in amplify. You need to keep urself alive when teleporting or standing. Mages wont do anything greatly. Revives over Mages. I would take Bul Kathos for life instead of mana. I would take Chancie glove for MF, war traveler for MF.. marrowwalk- +1 skeleton mastery isnt big deal. Dont need poison nova because corpse explosion will kill anything.. If you plan to use poison nova.. whats the point of ur summon/merc? I would have merc use Fort and infinity(Increases more damage for CE as well)so your merc can kill fast so you can CE in no time.
Just my 2 cent. I have played many different summon necro build.. this is best one for me.