Okay, fine. Shorter version.
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The default hero should be able to clear the campaign just fine. Wall Climbing should be among the first things you select at level 1, then mostly Def until Def is near 10. Then add a mix of Att, Resist, and some other abilities (like the movement abilities), and finally look into adding Dam and Spell Casting. You want Def at 10 (after considering your buffs and items) as second priority (first priority is Wall Climbing). 10 Att is another high priority so your leader can keep killing things. Res keeps disables from killing you, and Dam is actually really useful to improve. The movement abilities (Forestry, Mountaineering, Cave Crawling) are all important, and I think True Seeing and Vision 4 are both too useful to pass up.
I just finished a Keepers -> Elves run last night. I chose Lightning Strike, Hurl Stones, and Night Vision as my starting abilities.
-Don't spend starting skill points on anything you could buy at level up.
-Lightning Strike disables for 1 turn, but it has a good attack rate and doesn't dispel on hit. Cold Strike disables for 3 turns, but has a lower success rate and dispels on hit. Poison Strike and Holy Strike lower the victim's stats, but they don't disable. Fire Strike and Death Strike aren't effective enough to consider.
-Hurl Stones can only be bought at character creation. I firmly believe your leader needs a ranged attack; there are several flying units with ranged attacks that can kill any land-bound melee-only unit, and it lets your leader actively attack melee fliers instead of relying entirely on retaliations to kill them. It also gives your leader an alternative to melee, especially in the early levels when his defense is still low.
Archery (4 att, 2 dam, 2 hits) and Poison Darts (4 att, 1 dam, 3 hits, chance to poison) are both viable and can be bought after character creation. However, Hurl Stones (3 att, 1 dam, 4 hits) gets the biggest boost from Marksmanship 4.
Web could theoretically be used to deal with fliers, but it has a low success rate and opens you up to retaliations if it fails to work.
-Night Vision is a huge Quality-Of-Life ability. It lets you keep your full vision radius underground and while attacking ruins/crypts/etc. Adding Vision 4 means scouting the underground is no longer a chore, and you'll be able to pull crypt defenders to you instead of blundering into them in the dark. I've played with and without, and having it was indescribably nice.
-Other contenders for starting abilities: Regeneration (healing ability), Life Stealing (light healing, helps off-set attrition in a large battle), and Dominate (adds to your army, but you'll need to deal with morale and unit maintenance). I don't remember if you can buy Healing at the start, but that is also a really useful ability (probably more useful than either Regeneration or Life Stealing).
Swimming is only available if you create a Lizardman hero, but it would mean your leader can freely cross water (or take refuge on it), but boats, flying transports (Dwarven Balloon), Water spells, and Air spells can all help you get across water too.
Spell Spheres:
-You need a reliable way of healing your hero.
-Plan ahead. Don't spend skill points on things that magic can reasonably do for you (Reasonable: expecting to have Bless or Stone Skin always available. Unreasonable: Expecting to have Wind Walking always available).
-Air gives Haste (amazing, and can't be replicated by skills) and Giant Eagles (excellent scouts). Bird's View is also an okay spell if you have spare mana and spell points. Air Elementals and Wind Walking are available at higher tiers.
-Earth gives Stone Skin and Free Movement. Earth might have the best Mastery spell, if you ever get around to casting such. Entangle (T1) is a great disable spell if it works.
-Water gives Healing Water at T1 and Water Walking at T2. Liquid Form at T3 gives the lovely Physical Protection and provides Water Walking as a perk.
-Fire gives Fury at T1 and Fire Halo at T2. Fire Halo is one of the few ways to cross lava, and it is by far the most convenient way of doing so.
-Life gives Remedy and Bless at T1. Holy Champion is also nice if you can afford to maintain it. Rejuvenate can clear corrupted land around a city to allow it to start farming.
-Death gives Dark Gift, and T3 gives Animate Ruins. Unholy Champion is also nice.
The biggest choice is whether to take Air or Earth. I think Air wins out here, but I can certainly understand someone choosing the other way.
For my latest run, I took 1 Air, 1 Light, and 1 Water at the start. I added 1 Air and 1 Light when offered the choice, then 2 more Air when offered the second choice. The Water pick was kind of a waste, since Remedy could do most of what Healing Water did for me and I didn't go far enough to research Water Walking.
