How many AI units do you plan to spawn?
Simple way would be to create a very simple AI for the pawns, with another pawn telling the pawns simple commands for what it wants them to do. This would be the easiest to do. The problem with spawning a large number of actors into the level at once is the AI, as even if they are off screen the AI will still be running. Now you could make it so only when you are in a certain radius that the AI runs. Or only have the AI running once in a while when outside a certain distance.