Are those the best possible upgrades for this specific rig? Because I, sadly, know that 8 gigs of ram is the max.
I have the exact same computer and IMO I would upgrade the graphics card if you are looking at gaming. I am looking at the XFX Radeon HD 6670, but you can get any graphics card as long as it has the correct PCI slot. You will also have to upgrade the PSU most likely depending on what video card you get.
The only upgrade I have actually done so far is my CPU fan/heatsink (because the stock one is extremely loud) and if you do that you could probably also overclock.
The best possible upgrade depends on how far you want to go. Of course you could upgrade the motherboard the CPU the RAM and everything else, but it would probably be cheaper just getting a new PC. As I said before I would upgrade the video card, see if you want to upgrade it more then after that I would try to overclock CPU (or get a new one). Just make sure to get a new PSU for any upgrades that would consume more power.