BTW, Malkus is rather useless in this campaign. He didn't change an outcome of any battle and I am pretty sure that we would be fine without his aid.
The only thing I like in Ardent Debater plan is sending cult of the wolf away... And even here I don't think that North is the right direction to take....
Guys, how about doing this?
1) Send our smoke wraiths\spectres in, do reconnaissance of the area, see where their defences are strongest, and what assets this town has to bear
2) Carefully poke in the dreams of the citizens. Consider corrupting a guard or two should we find a good target
3) Consider summoning few black imps to prepare an attack from below if scouts will find that this route is good
4) Send Malkus, Cult of the Wolf, Brutewolves and Mkilzk to the lands of Ura tribes to terrorise the area, create more brutewolves\assemble army of regular wolves\war dogs and enlarge the cult by forcefully converting some of victims.
5) Undead part of the army to remain with you staying around the city and waiting for an opportunity to attack. Needless to say that any travellers to be killed
My reasoning here is > Brutewolves and humans have a bad habit of eating, preventing us from staying in the area for few months. In the same time, they are not very useful in assaulting the city. Also, they are way more mobile than zombies and even if we decide to skip the city and move further, their mobility is useless because horde moves with a speed of a zombie.
Malkus is good for leading humans and training them to fight, if we want to get a leader for the undead horde, upgrading a wight (maybe giving him the corrupted staff) is a better course of action