This doesn't answer your general questions, but I think the guys here have already addressed those better than I could.
However, since I recently ran across this LA Ermor AAR written by Calahan and you're playing against Ermor I thought this might be of interest to you:
http://forum.shrapnelgames.com/showt...033#post709033
It isn't a turn by turn DAR/AAR, it's more like a wrap-up of how his game went / how victory was achieved with Ermor. I thought it was a great read. It's interesting not just if you're interested in playing Ermor, but also in terms of what his concerns were - what opponent strategies / tactics might have potentially posed the greatest risk to his nation of undead.
You probably already know about Banishment and Cleansing Water, but just in case you weren't aware of how useful they are against undead, here's a breakdown of what they do at various mage path levels (hopefully I did my math right on these)...
Banishment (AN, resisted by MR, base fat 0)
H1 dmg 5; aoe 4; rg 20; fat 0 + enc
H2 dmg 7; aoe 6; rg 25; fat 0 + enc
H3 dmg 9; aoe 8; rg 30; fat 0 + enc
Cleansing Water (Evo 6, AN, not resistable, base fat 20)
W2 dmg 5; aoe 4; rg 20; fat 20 + enc
W3 dmg 6; aoe 5; rg 25; fat 10 + enc
W4 dmg 7; aoe 6; rg 30; fat 7 + enc
Of course, if you're using Amhazair's Bane Lord example SC/thug, it may not be ideal to have mages in the same army spamming low precision anti-undead spells. Although, with the decent MR of the Bane Lord you could probably get away with the Banishment spamming - Cleansing Water not so much. You could always just have the Bane Lord operate independently from your anti-undead magic spammers.
I feel like there are some great anti-undead spells that death mages have access to, but I can't recall what they are at the moment. In early/mid-game I mean (before undead mastery)..?
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Edit: rdonj beat me to the punch on Cleansing Water, and also answered my question re: Wither Bones.