The positioning of cleric in your classo will affect the range of supplicants at your disposal. Have a look at the helpfile for the full list and the level restricts on each.
Ne/Dr = Great mregen and fluidity spell but note you can't order your undeads while shifted.
Mo/Ne vs Ne/Mo - Having a non-caster class as second will hurt your mregen but it works for some people. That said, as a necro you consume a chunk of mana to summon and prep your pets. Regen gets tedious
Also, the order lag will be shorter for a Necro prime.
I haven't played a tank in ages but that classo is pretty popular for tanks because of wraithform and spectral shield. Having pets will boost your solo capability.