It will work, but you will have a bottleneck in badly threaded games (arma/dayz etc). I would get the gpu and see if you get the fps that you want, if not then upgrade your cpu. How much are you paying for the 660? You could probably get better performance for cheaper by going with an r9 270x or an r9 280.
If i disable the onboard graphics on my apu will it help the is function better as a CPU?
If the dedicated graphics are enabled, the onboard graphics should be disabled by default. It does help the CPU a little in the sense than there's less heat generated by the APU portion. Less heat means less chance of throttling.