If your characters were in combat mode and you had the warrior selected as leader, then the archer should have automatically started attacking if set to aggressive. The character in the lead is always under your control, so the aggressive setting will not matter.
Also, the act 1 summoning doll can equip a crossbow (the only doll that can use a ranged weapon), so can provide some support for tough fights. It would not last long if attacked directly, though.
You do not need a skill to use charms. The charm slot graphic in BD is the same as the closed slot graphic in DD, but you can just drag and drop charms in to the window to permanently add them to the equipment.
charm effectsVarious creatures have differing resistances or vulnerabilities to the different damage types, but none need a specific weapon/arrow to be killed. I collected the different arrow types thinking they would eventually come in handy, but ended up pretty much only using normal and power arrows (I used splitting arrows once against a group in a confined space, which seemed quite effective).
For warriors, I only put a couple skill points into the damage and accuracy portions of their weapon expertise, and that seemed to be good enough. I had my archer max Reload Time, as that gave a direct bonus to Speed.
For mages, more powerful and mana efficient spells (particularly shaman magic) start to become available in act 2.
I gave both my characters a couple levels of the healing spell, to help conserve potions, and my hero learned Identify. Lockpick would probably be handy, though I completed the game before the patch release that fixed that skill. Repair is handy, as is Sharpen Weapon (if you have the agility to meet the increased requirements).