I'm a survivor myself, I don't recall what level I was but I think it's less than 7... using a bow, I managed to clear all the beasties in the catacombs and solving all the quests in Aleroth before venturing out...
The hardest creatures I've met in the catacombs were the the skeleton lord with the flame bow and the giant spider, both in the catacombs.
Three words, run and shoot. Tough but I eventually took them down. Elven Sight(?) at level 2 helped get in a few more shots... the spider is especially tough since it moves real fast; the skeleton lord's flame bow stuns you, but liberal use of the pause and good range will win the day... not to mention patience and saves...
The hardest so far has been the Troll King... needed to "cheat" with that one, by teleporting just outside the cave to avoid his hits, then going back in via the entrance...
Skels summoned by conjurors are XP-less... they are distinguished by a white transluscent glow...
