Karazhan:
This was home to the Second Guardian, and powerful magician, Medivh.
Now it's inhabited by ghosts and memories of the past, and other horrors.

Location:
Deadwind Pass, southwestern side of map.

Mob facts:
Many mobs in the start usually don't hit a blue geared warrior for extreme amounts but it's advisable that you get some decent crraftable/BoE/Rep epics before stepping in to ease the strain on healers.

Healers should at best have 1200 bonus healing, around 150 mana regeneration while casting and around 7000 mana.

Caster DPS is mostly best to have around 600-800 spell damage in your current damage school IE. 800 frost damage if you're a frost mage. 8-9k mana at best. Around 6-7k HP required for some bossfights.

Melee DPS needs rather high HP Pool around 7-8k HP and 9k at best.
Decent crit (20-30%) decent AP (warriors 1400, rogues pref 1700, feral druids pref 1900) and hit cap (16% hit bonus).

Tanks REQUIRE above 11k HP somewhat around 18-23k armor, depending on class and decent damage mitigation.

With those stats you are actually ready to go on every boss apart Prince Malchezaar and Nightbane (more to that later).

A good group combo is;
2 tanks: Pref 1 warrior and 1 Feral Druid.
3 healers:
 - Decent Healer setups are:
 *Holy Priest, Holy Paladin and Restoration Shaman
 *2 Holy Priests and a Restoration Druid
 *1 Holy Paladin 2 Holy Priests
 *1 Restoration Shaman 1 Restoration Druid and a Holy Priest.
5 DPS classes:
1 Mage, 1 Warlock, 2 Rogues, 1 Shadow Priest.
or
2 Warlocks, Hunter/Retribution Paladin, 2 Rogues, Enchantment Shaman.

Hunters, Retribution Paladins, Mages, Moonkin Druids, is a good addition but mentioned class combos are better for high damage output.

Example of a group setup to boost perfomance:
Group Setup:
Party 1:
Party Synergy:  (Gains Bonus from Blood Pact and Tree of Life Aura) - Tree of Life Aura lets the warlock take more healing from Restoration Druids, thus can life tap more for mana regeneration. Also Devotion Aura for Tanks.
1 - Tank 1
2 - Tank 2
3 - Warlock
4 - Holy Paladin
5 - Restoration Druid
Party 2:
Party Synergy: (Totem Bonus, which increases damage by huge amount, Trueshot Aura from Hunters (AP increase) or 3% to crit from Ret Pala judgement, Unleashed Rage 8% AP increase, Blood Pact Bonus)
1 - Rogue
2 - Rogue
3 - Enchantment Shaman
4 - Retribution Paladin/Hunter
5 - Warlock

Though remember! As Melee is the best damage dealing class in The Burning Crusade, they have a lot of things to watch out for so it can cut down a lot of their damage. Suggest you find competent melee DPS, or else you should stick around with casters.

Every Tank, Healer and DPS should bring pots that boosts their perfomance as you kit up in Karazhan.