http://pcpartpicker.com/p/KRZzGXyou have less graphics cards power, but if LoL is as demanding then DOTA 2, it won't matter.
windows doesn't fit, unless you are a student, try to get it for free from school or buy it from the school's library for cheaper.
you could always get ubuntu or steamos, if there's a version of your games that you play until you can buy it or you could try windows 10 if you feel like it (
http://www.cnet.com/how-to/where-when-and-how-to-get-windows-10/ ) and buy windows 8.1 or buy windows 10 when it's no longer a trial.