Army

Only the following troops are limited to one piece: -Medium Cavalry -Knights Cavalry -Longsword Knights -Greatsword Knights -Greataxe Knights -Crossbowmen -Composite Bow Archers

The rest you can have as many as you want (even axemen and macemen).

Out of that: Having more than 3 of an artillery type doesn't make sense, because 1) you can't use more than 3 in your army and 2) they never get wounded, so no need to replace them.