From your messages it seems this is what you want
1) Number of non player race 0
This means NPR will not be generated at start
2) NPR generation chance by player > 0 (default is 30)
This means there is a 30% chance if you explore a new system that a NPR will be there IF there are habitable planets. . . this means at least in previous aurora that 30%->1 out of 10 systems, even less
3) NPR generation chance by NPR 0
So you control the creation of NPR
With this setup every time you enter a new system there is a chance there will be an NPR. you control the speed at which you explore so you can prepare as much as you want
Enjoy the game!
Aca