As some one who plays mostly offline single player this could help fill in some of those missing gaps. I have checked out both Simple Humans and NPC Humans and while they were close they do leave some things to be desired.
Since I don't mod games myself I have no idea what the difficulty modding things is, though I do have a little experience with general coding so I can respect its difficulty. That said I do have some suggestions that I would like to see.
The biggest suggestion would don't just have NPCs that you can "hire" at a merchant's shop, have some building their own little colonies - maybe have a few small buildings they inhabit - that you can "recruit" (knockout and tame) to your base. To explain why you can hire NPCs from the merchant you could just put in that they are looking for a new tribe that they can get being, such as being wealthy enough to pay them to join.
The next two are things about the others that could have improved them that I think should be in this one to really makes it the top NPC mod:
The big thing that ruined Simple humans for me is that the model used for them could not fit in standard vanilla doorways, as I wanted to populate my base with them. One other thing is that they could not gather anything. Though I did like its random name generator - each NPC had its own unique name. It would seem that these NPCs are able to gather and I don't think they are larger than the doorways.
The thing about NPC Humans that bugs me is that when you place armor on the NPCs it does not retain any of the dyeing you did on them while that does not ruin the mod it does ruin some of the in game customization you can do to make each one different. And as mentioned before I liked the random name generator and it is not present in this mod.
Just a few thoughts I thought you mite find helpful. Looking forward to how this mod develops.