4 quests

Onyxia attunement (Horde) — all steps

These tables are the Classic 1.12 baseline these hubs shipped with; Forever keeps them and layers new quests on top. Where Forever changed a quest, the row says so. Levels are quest level / required level.

Rexxar's part of the chain

QuestLevel / reqGiver → turn-inWhat you doReward
The Champion of the HordeXP only
The Testament of RexxarXP only
Ascension...XP only
Blood of the Black Dragon ChampionDrakefire Amulet

Baseline figures from the Classic quest database; Forever reward and XP values can differ after the October XP changes. Zone overviews: zones and map.