Some things written here are incorrect, so trying to clarify, I'm IT student.
If only thing you care about is stellaris performance:
RAM:
4 GB may be enough, but I would recommend at least 8 GB to any windows 10 system. Stellaris doesn't benefit from more but nowadays 16 is "optimal" if you like to keep few things like browser with few tabs and game open at once.
GPU:
Anything around gtx1050 is pretty much enough for 1080p, as stellaris is not very demanding on gpu.
If you have higher resolutions, gtx 1060, 1070 may be more optimal.
CPU:
as some guys stated, stellaris is pretty much cpu-heavy simulation where majority of calculations happen at one thread. That means you want cpu with as much single threaded performance as you can afford -> intel processors are nobrainer choice here
These are top processors on market, If you dont know what to do with money, buy i9 9900.
I would recommend i7 9700 as it is almost same but cca 130 dollars less.
Then there is i5 9600 which is best performance/cost ratio from high end cpus.
If you dont have much money, look for i3 or maybe some ryzen as those are cheaper, but you are losing performance here.
STORAGE:
While playing, SSD wont help with performance one bit, as someone incorrectly stated it will. Only thing SSD will help with, are loading times. While I would recommend SSD as system drive, it is absolutly not needed for stellaris if you dont mind waiting for game to load.
