So many of us experienced it. We don't have enough notes for our NPCs or we feel so underprepared. I hope this can help you. If it needs more work plz tell me in the comments, then I will try to make some changes.
I made two templates, a simple one for NPCs not needing a lot of a stats and a more detailed one with the most important stats.
I actually made these templates based on a previous post in here "Note-card NPCs: A quick and easy template for fleshing out and referencing your NPCs:)"