First and foremost, get 8GB of memory. 4GB will cause your system to page like mad, which will slow everything
down. 8GB is more than enough for years to come.
As far as the video cards, the 7850 has a nice lead in most games.
Also, one of the reviews on Newegg for that motherboard specifically lists the 3450 as having compatibility problems. I'd go with a board from one of the more reputable brands like Gigabyte, ASUS or ASRock.