The R5 1600 is an excellent choice, paired with a RX 580 or GTX 1060 6GB is a great build. For the RAM, you don't really have a choice you need to use DDR4 if you're using any of the modern platforms like Ryzen (R 1xxx) or Kaby Lake (Intel 7xxx). Go with 8GB minimum but 16GB if you're happy to spend the extra as a few games already will benefit from more than 8GB and this will only increase as time goes on. The i5 7600K, while a strong Gaming CPU is only a quad core with no extra threads meaning it'll likely fall behind very quickly over these next couple years as the phase shifts to 6+ Threads in Games. And since the R5 1600 is a 6-core with 12 threads you'll be much better off down the track. Overall with a R5 1600 + GTX 1060 6GB/RX...