21 wroteDefinitely don't get the FX-8350. If you were going with older hardware to save money, you'd be better off just buying a Haswell(ideally) i5.
I wouldn't have bothered with the GTX 660 either to be honest, not for a NAS anyway. Just use an APU, the Ryzen 3 2200G is perfect for a NAS IMO. That, or the R5 2400G if you want the extra 4 threads, but the 2400G isn't really worth the premium over the 2200G IMO. I suppose though since you have the GTX 660 anyway, just look at R3 1200 and R5 1400. There are plenty of first gen Ryzen CPUs on the used market, especially Ryzen 3 1200/1300x, so you can pick them up really cheap these days.
I'd usually advise trying to get a reasonably good quality motherboard for a Ryzen CPU, but as it's for a NAS and you'll only be using a 4 core, I'd just get the cheapest B350/B450 motherboard you can find tbh. Again, B350 mobo's can be found pretty cheap on the used market.
Whether you use FreeNAS or Win10 is up to you, it depends on what you want to do with the system. If it's just a NAS, then use FreeNAS. If you're going to use it as a computer, then Win10.
Lastly, both of those PSU's are trash. Don't buy either of them. Not sure what availability/pricing is like for you, but you should be able to get a Corsair CX450 for a similar price, which is a much better PSU.
Firstly, thanks for your help. I'll definitely pick up a the CX450, but I have one question.
Why shouldn't I get a FX-8450, when looking at benchmarks and the price both of these points are better than for example the Ryzen 3 1200/1300x or one of the i5 in the used marketplace. Of course it's old, but what's the disadvantage of it? The only drawback I see is the support for only DDR3-Memory.
Thanks in advance