Ok so i7: no, don't. The premium is significant for very little added performance in games. Your 4590 will still do for a few years most likely. And your memory is DDR3 by the way. GDDR5 is what is in your graphics card. More memory is certainly not the most pressing matter either.
The best upgrade for general purpose gaming is likely to be a better GPU such as the soon to be released GTX 1060 or AMD equivalent. Your setup is quite balanced as is so unless you intend to play at resolutions higher than 1080p, a CPU+mobo upgrade could also be worthwhile. Consider the midrange Skylake CPUs, i5-6500, i5-6600 and i5-6600K. I'm not sure AMD has very good products in that range right now.
Alright, I was also thinking about getting an SSD, is it worth it?
Yes. This is pretty much a no-brainer, forget about everything else. The 250Gb samsung 850PRO goes for less than 100$ usually.