Again, I'll emphasize so you don't f#$% yourself, that PSU you have on the build link is NOT sufficient for the GPU. You CANNOT use the PCPartpicker estimated wattage as it's never even close to the actual needs of the GPU much less the entire unit.
The Arctic silver paste really isn't necessary. The CPU cooler that comes with the CPU will have a thermal pad already applied to the bottom and it works just fine. If you were purchasing an aftermarket cooler it might be ok, but even then, all the MAJOR cooler manufacturers include TIM that works just as well, if not better, than the Arctic Silver.
The memory on that build IS CAS 7, so that's a plus, but it's more expensive and really won't add any performance that will be truly noticeable other than on benchmark scores.
The Sapphire card is a better unit than the MSI Twin Frozr, IMO. That probably doesn't matter either way though. Both cards are fine.
The SSD is nice too, I definitely recommend one, but not necessarily the V300 series. You don't need an SSD to game. The only thing that will improve is map loading. For other areas of computing though it's beneficial and will certainly speed up things a bit. It can be added later and have the OS transferred to it then if price NOW is an issue. If you have to have one now, I'd really recommend the Crucial MX100 over the Kingston though.
http://www.anandtech.com/show/7763/an-update-to-kingston-ssdnow-v300-a-switch-to-slower-micron-nand