Go for a 550 watt psu if you dont want to upgrade anything in future.
Or you can go with a 650 watt psu which will give you some headroom for future upgrade.
If you intend to sli in future go for a 850watt psu.
Go for seasonic or corsair except their cx series.
CX is ok for a low budget system that will not be overclocked. But if building a high end gaming build that will be overclocked, the CX lineup generally isn't recommended because if a concern on the quality of the capacitors used in them. That plus the fact that you can get higher quality PSUs like the one I linked for very reasonable prices.
Absolutely no problem. Where you would run into trouble is if you are planning on going crossfire in the future, which I assume you are not planning to since you have an Nvidia card selected.
hey i just realize the psu you mentioned is not available in my country.... i only can get seasonic m12ii s12ii and corsair