I built mine for $300 bare bones, CPU+MOBO+RAM and re-used most of the things I had until I could buy others, its possible to build a decent gaming computer for $250, just don't expect it to run things at max or high settings.
I would consider an ok gaming pc something that can run games at medium at a stable 60fps,then from there if you want something like better graphics or faster processing you then upgrade.
O really? Iirc basicly every dual core bottlenecks the stuff out of the GTX960
Guess not than.
Either way with quadcores you can upgrade it later on.
From what I know from Quadcore and above there is not much difference in gaming unless its a extremely cpu heavy game, gpu usually does more of the work when it comes to gaming, and Six and Eight cores can be overkill but if you can afford it I don't see a reason not to do it.