Just add a 4GB or 8GB stick of DDR3 to the system. Your return on investment with a 2x8GB kit won't be very good as you won't use more than 8GB RAM for gaming. Utilizing the 4GB stick that you have already is a good idea to maximize value.
Overclocking is not really a serious
option here on that motherboard. I wouldn't waste money on a CPU cooler unless it is with the intention of reducing system noise. The CPU cooler included with the FX-4130 is the heat-piped AMD cooler, and is more than adequate to run the FX-4130 at speeds far in excess of what that motherboard could reliably supply power for, so there's no overclocking benefit to a new CPU cooler here unless the motherboard is replaced as well. Furthermore, unless overclocking is a subject that interests you specifically. (Some people have more fun overclocking and bench-marking, than they do playing games, [guilty]), then you can leave this part of the system alone for now. If it were me, I would entertain the idea of seeing what could be coaxed out of the chip without increasing dissipation above "normal." Most of these chips have a little wiggle room to bump up the clocks a couple-few hundred mhz while reducing voltage, resulting in a performance improvement without increase power requirements. Whether or not you want to take the time to find a stable manual setting like this is up to you.
SSD is optional and won't effect what graphical settings you will be able to run at, only how fast the system boots and how fast the game loads and zones.
The GPU is the area that your system has the most to gain, and is where you will get the best return on investment. The HD7770 you have selected, is 6-8X faster than the HD6450 that you have now. No other component upgrade will result in as much performance scaling vs the investment cost than the GPU for your system. Though I don't believe I would select a 2GB version of the HD7770 personally, as there are likely sub $100 versions of this card with 1GB, which would work equally well.
For AMD options, depending on price and availability:
HD7770, R7 260, HD7790, R7 260X, HD7850, R9 270, HD7870, and R9 270X.
For Nvidia options, again, depending on price and availability:
GTX650Ti, GTX660, GTX760,
For the lower end cards in this range, 1GB VRAM is fine, as more would not be particularly beneficial as you would run out of render performance before running out of VRAM. Simply adjust texture/AA settings to run good on these GPUs and VRAM usage should be under 1GB anyway. On the upper tier cards, 2GB has more potential to be useful as there is enough rendering performance to utilize higher detail and/or AA settings that demand more VRAM.
I believe you will find that the best value exists in this range when paired with your existing CPU. More GPU investment than this is apt to be sullied by CPU bound scenarios. If you're going to be starting fresh with a system install to an SSD on this upgrade, then either AMD or NV are worthwhile considerations here, however, if you want to stay on your current install/HD, then I believe you would have a smoother transition to an AMD GPU, since your system should already have AMD drivers installed. For $100 after MIR, this is probably the best value option right now: PowerColor HD7790
The PSU is more or less a pre-requisite to the GPU upgrade. The Rosewill green series is an OLD platform. Not terrible but there are better options to choose from.
This modern design would be better: Capstone 450W
If you're interested in a PSU investment for the long haul of potential upgrades, learning to overclock, etc, then it may be worthwhile to invest in a bigger PSU at this time, otherwise, this 450W PSU is fine for any of those GPU's I listed combined with your current CPU.Edited by mdocod - 1/11/14 at 1:31pm