I am almost through act I in tactical mode. Hard, but not too much. In the start beef up agility at each level up. Skillwise, beef up Damage and accuracy for each character's favourite weapon and you should be ok.
I've managed so far even though i screwed up: Offensive magic sucks so far, my hero mage wannabe has put 4 points into focused elemental missile, but the damage is too low and the mana cost is too high to be worth it. So he's fighting with a weapon instead. If you do not waste skillpoints as I did you should fare even better.
