Magic items make for a poorer world flavor wise.
An item of Deathward is obviously something that would be priceless on a mission like this, blocking drain of ability scores and levels. - But, unfortunately I do not even dare ask for it, since I get shot down hard every time I being up that items could sometimes be nice to have as part of your character.
At adventure level, our ECL and actions will count. Not which items we bring, unless near artifact type items specifically for the task at hand. - Like the Sun Sword is obviously strong vs. undead, it is not overwhelmingly so.
As for a local guide, Daouta's, or maybe just the ruling line, can locate the lair just by trying. Shadow world stuff... Well, thats not my forté, but I find it given that it will be involved, since a large numbers of troops are currently not possibly to find in our world.
Oh, what did you say about Osoeriene? - You got censored.