A good stealth/warrior build would be:
Archery / Stealth / Critical Strike
(Melee weapon) / Dodging / Backstabbing
Streetwise / Pickpocket / Swimming / Mercantile / Climbing / Etiquette
Advantages: Immunity to magic, rapid healing, bonus to hit undead
Disadvantages: Inability to regen spellpoints in light, Inability to regen spellpoints in dark
With this setup, you don't need Intel or Willpower at all, so you can drop those down to ten each, and stack up the stats you like to the sky. Get some strength and agility.
In the character creator you have an option to answer ten questions about your character. Choosing the options gives you a boost to whichever thing, so say you practice stealth, that you've been dodging for a long time, and especially that you have an ebony dagger. With the ebony dagger, you can slash through the enemies like they're chumps.
If you still have to run past enemies, there is a hidden door behind the bat in the large throneroom at the base of the stairs. Go in there and run straight forward, and there is a passageway that lets you get into the upper part of the dungeon near the exit. The exit door is black with gray stone and a skull, inside a room with one bat, one rat, and an imp.