[Agema]

How big your army needs to be is a judgement you have to make yourself. You'll need to reanimate with priests early on to get your armies going. Once your Dom develops, you can let the freespawn do all the work.

Your armies will need to be bigger than equivalent non-undead. Longdeads have half as many HP, their armour is rotted/rusted to about 80% effective, and they often have bad equipment. Savour your Ermorian specific undead, longdead legionaries etc. for this reason, as they are reliably well equipped. Soulless are tougher and stronger, but have dreadful Att/Def values.

If there's no priest around, you'd probably want about twice as many longdeads/soulless as you'd use humans. Once priests start arriving, your troops can be annihilated at an astonishing rate, so you'll need vast, vast hordes.