Jann offers very good advice.
Workstation tasks put tremendously more stress on the PSU than anything else. Both your CPU and GPU will often work at 100perc. , in their upclocked turbo rates and the least thing you want is instability. At best case, your PC shutting down during rendering, at worst case, your PC going up in flames :- ). Not even kidding.
If you are from EU and need to save some money, you can buy fully legal refurbished Windows licence through ebay (since reselling licences is legal in European union). Windows 10 Pro goes for 6 euros..
But never save on PSU. Reputable brand with bronze rating will go long way. You can go for budget PSU brands like EVGA, and models with attached cables to save money.
Also because the price difference between 500W and something like 650W is often very negligible, it's good to go for the latter capacity.