Short answers, pulled from the story.
The first Army of the North was created on the 14th of December 1791, when the government of the Kingdom of France appointed the Comte de Rochambeau as its commander. It officially ceased to exist on the 25th of October 1797, when its troops became an occupation force in the Batavian Republic.
Jean-Baptiste Jourdan commanded the right wing of the Army of the North at the Battle of Fleurus on the 26th of June 1794. The victory led to the collapse of the Allied position in Flanders and Austria's loss of Belgium.
At its peak, including reserves, Napoleon's Armée du Nord numbered 130,000 men during the 1815 Waterloo Campaign. It fielded 344 artillery pieces and more cavalry than French armies had in the campaigns of 1813 and 1814.
Jean Nicolas Houchard won the Battle of Hondshoote in September 1793, forcing the English to abandon the Siege of Dunkirk, but the revolutionary government arrested him for failing to press his advantage after the victory and had him executed.
The Army of the North in Spain, formed in January 1811, was tasked with garrisoning cities and fortresses in northern Spain, fighting guerrillas, and keeping the roads to France open. Only 800 men from the army fought at the Battle of Vitoria in June 1813, after which it was absorbed into the reorganized Army of Spain.
The Army of the North suffered from low morale, severe supply problems, poor troop quality, and harsh winter weather when it was forced into open battle at St. Quentin. Its commander Louis Faidherbe was also too ill to command effectively, the result of decades of campaigning in West Africa.