The first set of stairs is deceiving, there are Laughing Skull rogues lurking in the shadows so let the tank first and warn everyone else about them. Chances that someone will pull extra mobs and wipe the party are medium, depending on how you decide to do the pull. The first pulls are relatively easy, I believe there were harder pulls in Scholomance in terms of mechanics and class usefulness but maybe it's just me. It could benefit from a classical tank and healer combo, a mage for some crowd control which can be quite important, perhaps a warlock for a few banishes and another support healing class and an offtank in case things get complicated. The instance isn't hard done the right way and with a decent setup.
Disclaimer: I've not assumed level 70 players were clearing this instance but the old school way as this guide was written when BC came out
