It really depends on what you plan on doing. If you're using youtube, most new processors will be good enough to play the HD videos. You also have to consider the resolution. If you're doing 720P gaming, you'd be fine with an I3 and a lower tier GPU. If you're doing 1080P gaming, you'd need an I5 and a medium or high tier GPU. AMD is okay, but get an fx 6300 and above if you're gaming.
I know this is alot to ask but could you recommend or list products that would be good, and how I get Windows 7 instead of Windows 8? I'm kinda a noob with this stuff so any help would be greatly appreciated