Consider your Populum pretty self sufficient to know when they are needed. They will appear by themselves WHENEVER a a justified war is fought, and will head on all by themselves. Consider them always on in times of war (like the coming invasion). If it will make it easier, I will add them to the stats, but remember that you have very little control over them, especially in times of peace.
And they are less than about 1% of the population - which makes them great for a future elite nobility class.
Conversion is mostly useless. The world currently is very accepting, and religions are served depending on location more than faith. Everyone believe all gods, at times as different gods and at times as just the image of a god known to them. Religiously things are very peaceful, no real war anti-others religion appeared yet...