For combat I'm focusing on melee weapons (I'm currently rank 3 in that skill, in addition to being rank 2 in dodge). My current companions are Virgil and Magnus, and yes, I always have a good number of fatigue potions. I've considered getting the harm and healing spells, but I'm thinking that my jolt spell and melee skills are enough for doing damage, and Virgil has the healing situation covered. Plus I don't really like the other skills in those colleges. If I were to spend my character points on spells, I was thinking I'd spend them on Resist Magick and Disperse Magick. Would you recommend doing this, or do you think I'd be better off just using them for willpower?
It wouldn't be my first choice. The number of situations where you'd want or need to disperse a spell can be counted on the fingers of one hand: Entangle (which prevents you from moving around, and reduces your attacks by one per round) and Weaken (which reduces your strength for the duration of the battle). Both of those spells automatically end when the encounter does, anyway. And most monsters either don't use magic at all, or use non-dispersable spells such as Fireflash or Stone Throw.
All that the Resist Magick spell does is augment your MR (magic resistance) which can also be done through certain magic armors, and wearable items such as the Dorian Amulet. A higher MR does somewhat reduce the damage done by magical creatures and traps, but so do more specific resistances such as Fire and Electrical.
In fact, IMO the only advantage at all to taking the Meta college is to take advantage of a glitch which can make magically charmed followers into permanent ones. I won't spoil how here, but if and when you're interested, google "Arcanum meta abuse". (I don't recommend doing it for a first playthrough, in any case.)
If you're a fighter yourself, consider the Temporal college as an alternative. Hasten doubles your PC's speed (and thus your attacks), while Tempus Fugit gives your entire party a +10 speed bonus, while giving your opponents a -10 penalty. Of course, you'll no longer be able to go on trains... but once you have Teleportation or access to a ship, that ceases to be a problem anyway.
As far as Jolt goes, its power doesn't increase with MA to the extent that Harm does. At or near 100% MA, Harm can actually deliver MORE damage, and at half the cost per casting. It's so powerful that it's been described as one of Arcanum's game breakers.
(Later on, you'll have the opportunity to become the master of one spell college; the only prerequisite is that you have to know all five spells in that college, and then pass a test. One of the perks is half-cost to cast the spells of that college. If you do this with the Force college, Jolt becomes as cheap as Harm; but if you do it with Dark Necro, you could pretty much sneeze out Harm spells all day!)