*Here's a BUILD recommendation (USA?):
http://pcpartpicker.com/p/wYbJmG
You may not like the case. I didn't do much research. Get one that has:
a) front USB3, and
b) at least one fan
Windows 8.1 is a definite yes, but I also recommend Start8 and tweak to avoid the Charms Bar in the desktop and boot direct to the traditional desktop.
*The total price is about $767. If you used the i5-4690K instead which is $240 (versus $75) it would be about $932 which is a lot more.
MOST games would not benefit too much from the better CPU, but some would and that will only continue into the future; Battlefield 4 for example can use use almost 100% of the i5-4670K's processing power at times. However considering the G3258 is only $75 you could always REPLACE it later if money is tight now.
It's going to depend a lot on the games you plan to play as well. If mostly older games which is fine because they're often cheap on STEAM (Skyrim etc) they'll generally run great on the G3258. There are again some exceptions. Metro 2033/LL is very demanding on both the CPU and the Graphics.