> Getting to the stairs was hard enough. From the moment I step through the door leading to the corridor, large groups of monsters await me on three successive spaces. This uses up nearly all spell points from my Wizard and two Sorcerers.

Try running through one or two of these monsters. That will save you the spell points you'd need to use up to bust through them.

> When I get to the stairs, I can't really do anything on level 6, so I go straight to level 7. There I have managed to map only a very tiny portion, as I keep running into Mist Wraiths, Zombies and Evil Eyestalks who seem to be completely immune to offensive spells.

Sorcerers know a few offensive spells that inflict unavoidable damage. Check the "Show Details" page of the spell lists, and you'll find out what those are. Also, for monsters like Mist Wraiths, do not underestimate the effectiveness of the QUIET-brand spells that Wizards know. High wisdom helps greatly in casting these spells effectively.

> Human Wizard, level 12, Human Knight, level 12, Wind Elf Rogue, level 13, Rock Elf Knight, level 11, Troll Sorcerer, level 7, Wind Elf Sorcerer, level 11.
>
> What should I do? Keep battling monsters on level 5 or try another approach to get further on levels 6 and 7? Or even dare to go to level 8?

I wouldn't be in such a rush to handle that area on level 7 yet. If you are successful early, that's fine, but it just means you'll still be behind when you get to the next step. So I'd take some time to level up a bit. At the very *least* get one of your sorcerers up to level 12, as he'll probably learn a strategic spell that should help you out quite a bit in that level 5->7 plunge.