Nothing particularly wrong with AMD chips, intel just blows them out of the water when it comes to gaming. If you want to game for as long as you can without upgrading, you want the i5-3570K and a 670. You can overclock to increase the life and add a second 670 in a few years when it can't keep up anymore.
8GB is plenty. 8GB will let you play a game and have a browser with a lot of tabs open. You won't really need more. An i7 runs EXACTLY the same as the i5 in gaming. You only want to get the i7 if you do pro work like photo editing, video editing, etc.