One thing is true when your army already has +300 men and you have to pay their salaries, many days of peace seem eternal, perhaps the balance to have many more days of peace should come from the fact that your cities and towns give you much money in tax form.
TW could include messages such as "the harvest has been success this year and X dinars have been collected" or the opposite, just as you as the lord of your lands, live from them and not from looting of the dead.
New mission for you once a year, collect your own taxes or send one of your captains with escort.