Also will i be wanting to upgrade processor or anything in the near future? How long until mine is too outdated?
I think you will. You'll know when it's time, when you're not happy with the game performance. You should be OK with D3 with the new graphics card I think.
And no - you won't need a new PSU when you change CPU/MB if you get a decent one with the new graphics card.
Corsair cx600 is about right on power - lets check options/prices.