yeah they spawn one by one. each time you hit F7 a new one spawns. i didn't set a limit - the limit is how much your computer can handle!
it sort of gets bothersome when you have more than 20, though. theyre all following niko, and they all try to get as close as possible when theyre not shooting. that means everybody bumps into each other and stuff. also for some reason when there are a lot they might begin turning on each other :p