What skills should Necromancers take when facing Orcs on a very large map?

Hmm... Well, don't say they're not different. What about the lack of retaliation?

Besides, you didn't answer my question:

What if those same goblins, which the shamans use to gain mana, are simply killed right away? What will you do?

Even if the shamans go down first, they'll only have enough mana for about 2 spells. And it's easy to predict that you have Daughters of Heaven in your army – just take a look in the tavern.

Furthermore, you didn't consider that this isn't even the Necromancer's main hero.