You can't overclock CPU/RAM in a H370 mainboard - you need a Z370. DDR4 is lmited to stock 2666 speed in H370.
750W PSU is wayyyy overdosed for this system - 400 would be sufficient (PSU load in the 60-70% region under gaming) but 500-550 gives more headroom for a big gfx upgrade.
Seasonic has some new and very good 550W Gold series PSUs
SSD is a must-have today at least for the system drive - a 500GB MX500 offers sufficient space and may host some of your most beloved games. Just for system a 250GB version is large enough but don't go smaller.
And one would need to overclocking for AHIII why? Overclocking increases the risk of instability on any system, unless you really know what you are doing in terms of setting voltages, clock rates and understand the CPU architecture in use; not to mention you need to do substantial cooling just to keep things stable and cool. A game like Metro or Witcher sure, AHIII ... not needed at all. In fact, it may cause more problems than it's worth, and lower the lifespan of the computer overall.
Mind you, this is coming from a guy who builds high end water-cooled computers for gamers for income. Personally I use dual Xeon workstations and Titans. One CPU handles the game threads, the other handles PCI tasks. Don't need to OC when you have horsepower and RAM and VRAM in quantity.

The system the OP has is fine and really no tweaks other than a better supply.