Windows 7 & 8 make the biggest difference in BF4, in other games it's up to you to decide whether you like 7 or 8 more(check google for reviews). I didn't say that you shouldn't buy 770 and 8.1, it's just that my personal choice is 7 (I've heard that 8.1 still has some issues that need to be fixed).
Yes, 2GB of VRAM is enough if you are going to play on 1080p. However, Minecraft is a CPU demanding game and 4670 should do a good job. Youtube videos show >120FPS(with fraps) using 4670 on Minecraft.
Btw, if you are into overclocking then go with 4670k.