Why the rush to gunpowder?

[Quillan]

holy crap...you need to have the highest archer building and then convert them using gunpowder, right?you get whatever their gunpowder counterparts are?

No, actually the gunpowder infantry are built in cities. The Militia Barracks (the one that gives you militia pikemen) enables Hand Gunners once the gunpowder discovered event occurs. There are two barracks above that: the Army Barracks (12,000 florins and 6-7 turns build time) and the Royal Barracks (15,000 florins and 8 turns). Before gunpowder they don't really do anything except possibly increase the recruitment pool of the earlier troops. After gunpowder, the army barracks enables arquebusiers and the royal barracks enables musketeers. You can build the barracks before the event, so you'll immediately be able to start recruitment when it happens, but the recruitment pool takes time to fill up.

The cannons are a separate line of buildings: gunsmith, cannon workshop, cannon foundry, royal armory. They can be built in cities or castles.

[dopp]

Does the royal barracks do anything for factions without access to musketeers? I never noticed.

From what I understand, Chinese warfare after the adoption of gunpowder (Ming thru Qing dynasty, although you have grenadiers and bombards as early as the late Song) was surprisingly similar to European warfare. Heavy lancers, musketeers, pikemen, 'sword-and-buckler' men, field and siege artillery, extensive fortifications (war wagons and fortified cities). More unique elements would be archers continuing to serve alongside the gunners. Maybe someone better versed in this stuff would know more.

[Quillan]

Factions who don't get musketeers cannot build a royal barracks. It's one way you can tell them apart. Byzantium doesn't even get to build an army barracks, since the only gunpowder troops they get are bombards.