Selecting magic paths on your pretender should be consequent to your overall goals for the game. For instance, if you have a nation with sacred troops that have a lot of health, taking a high nature bless will give them significant regeneration. Or, there might be a global enchantment that you know you want to cast because it will help your nation- (for instance, Gift of Nature's Bounty). You might want your pretender to start with nature 6, so that you only have to forge a +1 nature item for him to cast it. Rainbow pretenders operate on the same principle- they're not only great for site searching, but they can also cast a wide array of battlefield buffs, forge a large number of items (including excellent and useful cross-path items with high path requirements like the Chalice or the Gate Stone), or cast cross-path summons. All of these things might be possible with recruitable mages that are empowered or given path-boosting items, but will be more difficult.
As for mage support: decide what you want your mages to do, and construct them accordingly. Don't build a mage with items without having a plan for what you want them to cast. If you don't have national access to earth mages but you know you want to eventually be able to cast Army of Gold, then find a way to get an E2 mage, forge him Earth Boots and Armor of Earth, and send him with your army. Also, there are *many* path-boosting items, and you can give your mages a surprising boost to their magic power if you plan what items to give them beforehand.
I'm not entirely certain how it works, but there are algorithms the AI uses to determine that, in certain cases, your scripts will be ignored. I know that if you have mages scripted to cast spells that require a large number of gems but then encounter a small army that you can easily defeat, it will conserve your gems and cast less fatigue-intensive spells. Similarly, if you don't give your mages the required gems to cast high-fatigue spells, they obviously won't. This may be why your Prince of Death didn't cast Shadow Blast.
Animate Dead vs. Animate Skeletons- the former will give you Soulless (zombies), the latter will give you skeletons.
Undead can gain afflictions. They do have eyes. If you give a zombie a nasty chest wound, he'll have difficulties getting around just like a normal person, he just won't feel the pain. And undead cannot heal afflictions through the healing ability; I think the only way to heal undead is by using the Chalice or casting Gift of Health.
Archers alone are of limited use. They'll do significant damage to units with low protection. Units with high protection or with shields are rather archer-resistant. And then there's Arrow Fend to pretty much negate their effectiveness. But cast Wind Guide and Flaming Arrows on massed archers and watch your enemies drop.
Hope this helps.