The Army of Meridia is an umbrella quest for the whole of Coldharbour. On accepting the quest, some map markers were added - in the west, The Moonless Walk, and in the east, The Black Forge. Completing the quest chains at The Moonless Walk (and then The Lightless Oubliette) and The Black Forge (and then The Great Shackle) is the minimum you need to complete the quest.

However, your journal also says you "should also watch for any of the other missing Fighters Guild and Mages Guild members, or anyone else who can help me". This is a clue towards the objective Restore the Hollow City. The more side quests you complete around Coldharbour, the more the city will be restored, and the more allies you will have when you get to the final battle.

See the following pages at UESP for more information:

• The Army of Meridia, for general information about completing the quest
• Coldharbour Side Quests, for a list of the side quests you can complete
• Restoring the Hollow City, if you are not wary of spoilers and want a list of all the allies and where you can find them