If you can stretch your budget by another RM 300 then go for this, should be able to last you quite a while provided your requirement is not that high.

Intel Core i5 6400 - RM 779
Gigabyte B150M-D3H (D4) - RM 403
Kingston 8GB DDR4 2133MHz Value RAM - RM 196
Asus GTX960 4GB GDDR5 Turbo - RM 927
WD Blue 1TB HDD - RM 215
FSP Hexa+ 550W - RM 188
Thermaltake Versa H25 - RM 185
BenQ GW2270 - RM 429

Total: RM 3322 (ETech price inclusive of GST)

If unable to spare the extra RM 300 then either downgrade the i5 to i3 6100 (RM 485) or GPU to GTX950 (RM 699).

Cooling system? CPU comes with stock cooler and the case comes with 1 rear exhaust fan, add another 2 casing fans in front as intake to improve airflow, casing fan is not included in the list yet.

Of course can but if only for gaming then i7 won't benefit you by a large margin compare to i5.

That's 2GB vs 4GB, of course the 4GB one is better and will have advantage when the game uses more than 2GB VRAM.