[PvK]

I think Death magic can get him Spectral Mages (who have some random magic skills) which can (eventually with luck and forged boosters, maybe via Streams from Hades?) get him Unfrozen mages and maybe an Ether Lord.

Zweihanders vs. heavy shield infantry - the shield infantry are the sturdier block, but Zweihanders can do higher damage to penetrate with. I tend to use a few Zweihanders starting behind the main body of shielded troops.

Pikemen are faster to recruit and good for staving off lower-morale troops, so yes they might be a reasonable choice against giants. Better than the shielded heavy infantry, anyway.

Villains? Faster to recruit than the crossbowmen, and usable for light stealthy raiders. Their low morale and protection are major weaknesses though.