Ive noticed that some monsters seem to spawn out of nowhere and have to be watched, but i cant seem to find where they spawn from. Do they spawn form nodes? lairs? both or none?

Both, in fact, as well as from neutral towns. Leave no city unguarded!

Put towers on the list too.

Nodes/Towers will stop spewing rampaging monsters once they've been conquered. (and lairs/dungeons straight up disappear)