There's an increase in performance from DDR3 to DDR4, whether or not it's worth your money is up to you. Medium-high speed ram at 16gbs is what you're looking for. Unless you decide to get into rendering mass amounts of video. Minimum high end i5 if you're going with intel. Honestly you should strive for an i7 if you can, just be aware some i5 and i7 are alike but their prices are not. For average gaming go for 4-8 cores. If you're not planning on overclocking, water cooling is somewhat overkill.