The way I run as a mostly peaceful nation:

I have a small pool of professional soldiers. Before the increase in the musketeers, they totaled 1,000 troops; now they total 1,250, and some may die soon. Most of the army comes in the form of armed militia.

This is reflective of feudal times. You didn't see armies of men wearing full plate and carrying nice metal swords and shields. For one, that's heavy. Also, it's really expensive to field an army so well-equipped. Instead, you'd have a pool of professional soldiers, such as, yes, a house guard, that really did make a living out of warfare. Knights and huscarls are prime examples of such men. However, large professional armies didn't really become a "thing" until much later; a local lord would just gather up a bunch of peasants from his fields, equip them with weapons, and march them off to war. (Consequently, you usually saw a lot of people running away and deserting their armies in battle. This sort of behavior continued well into the 1700's. The Revolutionary War in the U.S.A. is riddled with examples of militia running away as soon as the enemy closes in on them.)

Making sure your armies are well fed and such is important. Most casualties in war have historically been from disease and injuries not being treated properly, so keep that in mind. A healthy, well-fed soldier is less likely to succumb to disease than a malnourished one.