3GB of RAM is fine. As long as you have something more powerful than current gen of consoles you will get good use out of it.
R9 280X is good if you want power on a budget. It gets 60FPS at 1080P in nearly everything. However you have to spend a lot more money if you want better than that.
If you think you need a better future proofed system the mythical R9 380X is finally coming at the start of November, and should get performance that is very close to the R9 390 and Nvidia 970.