Both NPCs an players take 1 spot on world map. But the formula for buying/enslaving NPCs is (CH-1)/2, so you can have only 5 NPCs at most, with magnetic personality.
You didn't mess anything, even number of CH is better IMO, unless you take 1. You can get +3 CH with drugs and you need this bonus only when acquiring new followers. With 4 CH and magnetic personality you can have up to 4 mercs. All you have to do is take mentat and beer when you will be buying them. Just remember without drugs you will be able to lead only 4 people/npcs.