One thing is clear: you shouldn't choose Lethos against Necropolis:

Still, my choice against Necropolis is Iranna.
Education from the start won't hurt, and neither will mana regeneration (Necropolis has Spiritual Link, and they have a large army, so you need a lot of mana). I'm not even mentioning the 1.5x stat boost.

Necromancers are not the fastest or most proactive troops, and Furies under Iranna, along with the corresponding Phantoms, can cause a lot of trouble.

+ The start is relatively easy, and, importantly, it's not difficult to throw enough creatures into the pit for +1 Fury (which is very beneficial in this case) + you can catch Kifrah (+250 gold and leveling up to the point of gathering troops - another +2 valuable Furies).