Ok well first off, with that motherboard you can't overclock. Therefore I would suggest getting the i5 4670 non K version. The K version is more money and you won't benefit from it on that motherboard. Even if the H81 chipset allowed overclocking, it would be inadvisable to anyway since there aren't any heatsinks on the VRM's.
Your PSU is fine, plenty of power.
If you are looking to improve your system performance (not just in games), consider getting a SSD in the 240GB or greater range. It won't improve gaming, but if you put your OS on it, it will boot much faster and be more responsive in general. Then put all your user files, games, and applications on the HDD.