Some questions for the more experienced players;
1) So far I've been mainly relying on swordsmen and bowmen/crossbowmen for support. What are the redeeming qualities of the other units? Because they all seem quite weak in comparison
I think how valuable the different units are, depends greatly on the overall situation of the current game and the strategy you've chosen to beat it.
For example, as strong as the units mentioned by you may be, if you don't have acces to their related ressources, they not only are quite expensive, their price and the price of everything else related to those ressources rises, every time you hire one. They also only have one movepoint, which cuts down the mobility of the hero's group they acompany. That will cost a lot of otherwise useable turns, over time.
For the strategy part, two examples:
Militia can be useful later on, to sacrifice them for those high death- and chaosmagicspells. Walking fodder for the dark mages.
The low cost and upkeep of bandits and thiefs allow for a quicker start. They can also be usefull if you want to play evil, and rely rather on many heros that roam plundering through the lands, than on a steady goldincome through rich provinces.
3) Is there any benefit to playing evil? Oppressing your population, sacrificing them for mana, raising them from the dead to fight for you, taking their stuff and money. So far the only real benefit I've seen is getting more money from events, at the cost of your people hating you, revolting against you, and stunting your economic growth.
I'm not that experienced either. In my current game i tried to take the evil route tho, and so far it works out well. The trick might be to choose individualy wich provinces you want to keep... and wich you want to bleed. Both can be profitable.
Summoning undead and demons (in battles and on the strategic map) is very powerfull! If you have a specialised mage, even more so.
Those who stay, cost no goldupkeep whatsoever, just gems. Which allows to use both of those ressources to the fullest, if balanced right. To be able to summon such permanent units in every province (or with a necromancer even in battles) to fill up slots, can also save a lot of otherwise wasted turns.
4) How do you deal with some of the tougher monsters? I tried to kill a few ogres the other day with a warrior that could cut his way through an army without breaking a sweat, and he got smashed to a bloody pulp before even seriously hurting one. And what is the trick for giant slugs? I can handle one or two, but any more and their spit just melts my units before they get close.
Those damn slugs... I found what works best (at least in the beginning of a game), are units that are immune to poison. Undead or gargoyles, for example. Especialy skelletons, which are available very early and also have a high ranged defense.
In my current game i started besides two lizard swamps. Not much else around, no ressources at all. I wanted to ally them as quick as possible, to get good meeletroops i could afford.
Of course for that, i had to kill 6 slugs first. So i picked the summon undead ritual and garrisoned every zombie and skelleton i got in my castle, until i had enough for a complete army. Luckily, by the time i got enough, i had found some places with enough slugs. 2x3, to be more precise. And even tho my heros where still very weak and i lost most units, it all worked out rather fast.
For the ogres... I 'm not quite sure. If they have low magic resistence, spells might work well. Even rather early ones. For example blindness, which is only level 2, but can take away all attack power for some turns.
EDIT: Ah, i got ninja'd.