If I was going to start a new game I would begin with both characters as warriors, since the more effective spells (like Shaman magic) only become available starting in act 2, there isn't easy access to arrows very early in the game (though it doesn't take long start collecting them), and melee damage works well. Actually, in my first game I collected special arrows and weapons with the intent to switch to an opponent's weakness if I ran into trouble, but practically, I never swapped weapons and only switched arrow types once (splitting arrows work well against groups in confined spaces).
In my first game I made my hero a crossbow archer once I got through most of act 1. Before that he used a club / walking stick most of the time, and switched to a bow/crossbow for tough fights. I left the DK using a sword (two handed once they became available).
Playing again I would have my DK be a bow archer, so he could concentrate more on agility, since he doesn't need strength for armour requirements. I would have my hero be a warrior, probably using swords. Early in the game one would use crushing weapons, since that is most effective against skeletons, and the DK would switch to a bow at some point between getting access to the battlefields (to build up a supply of arrows) and reaching the citadel (past the undead opponents of the start of the act, when crushing damage isn't an advantage compared to piercing).
For an archer I would switch to power arrows as soon as possible, but otherwise stick to normal arrows (occasionally splitting arrows). A warrior can also be fine with just a conventional weapon.
For weapon expertise skills, I would highly recommend maxing the bow's Reload Time sub-skill (gives a direct boost to Speed), and putting a few into Point Blank. Other than that, in my first game I was fine just putting a couple points into the damage and accuracy sub-skills. I was trying to conserve skill points so I could switch weapon types, try out traps, etc, but never ended up doing so, and wasn't hurt by being stingy with the skill points.
There is an overview of skills in an appendix of the
Beyond Divinity Strategy Guide, but not a dedicated build recommendation. Various suggestions about effective skills and techniques are made throughout the walkthrough portion, though (if you want to read up to the point you've already played, to get help or check if you missed anything). The math appendix does make some suggestions on stat point distribution, etc.