So here is what I am thinking as a build not only for playing through the Dawnguard faction, but also something versatile enough for the Main Quest, College of Winterhold, and enough utility for all around play.
Race: Nord (for role playing purposes only - I think Bretons would be a strong choice as well)
Main Skills
One Handed - dual wield perks,
Restoration - turn undead, healing is always useful, necromage perk
Archery - crossbows! Need a ranged option for combat
Smithing - someone has to smith those new dragonbone weapons and my light dragon skin armor.
Minor Skills
Enchanting - for making better weapons and armor
Stealth - sneaking around crypts and stealth attacks
Alchemy - never really used it before, but it seems to fit with the lore of the Witchhunter and allows for a range of buffs and poisons
Light Armor - not too many perks in this, but enough to add to my armor rating and still stay stealthy
Suggestions? Modifications?

