I'm pretty new to GMing, so I don't know how people do it normally. The last NPCs I created was purely to please myself and they are supposed to be powerful, so I tossed stats pretty freely, without really following any creation process. I was still trying to make it coherent.
What I'll do for NPC supposed to be reachable is look at the stats of PCs and making the NPCs slightly better if they are less than the PCs, or slightly weaker if they are a lot of them at the same time.
I don't if the high grade grunts they give in the corebook are useful ? Or do primer runners roll them over ?