If you’re using a sword you can put a shield in the other hand and have more armor, or you can put a smaller sword in the other hand and have two attacks. This initially makes your attacks less accurate (or maybe isn’t allowed at first, I don’t remember) but ambidextrous fighting is a skill you can level up with.

The better pole weapons do more damage than the better swords, and at higher levels you can also damage the enemy next to the enemy you’re attacking with a pole weapons (this might be it’s own bonus skill too, I don’t remember).

That party makeup sounds like what I usually go for. I eventually try and have everyone have some decent archery skill, and at least one level of Priest spells, so that everyone can cast minor heal.

Later in the game I try and get my mage to level up as a priest as well, so they can revive unconscious characters. It’s nice to have two characters that can do that.

To divide the potions I think you hold down shift then left-click with your mouse. I guess this mechanic isn’t just an Avernum thing, I just started The Legend of Grimrock and it’s the same there.