The best way to judge if your party is ready is to go through the *spoiler* Wizard Isle and Werewolf Isle and see how you do there... There aren't many hard fights in Durlag's but the major ones are probably among the toughest in the game...

Just curious why put all of your points into stealth when there is gear like the shadow armor and the boots of stealth so easily attainable??? Do not the two of them jump your stealth up 65% on their own?