What size PSU? How much you want to spend on a case? What size SSD? Lastly it makes more sense to buy a 1TB disk, rather than a 250GB - the price difference is not that much....
Ok firstly you'd be wasting money on a 760, rather get the 750.
Use that money for 8GB as it makes more sense with the P55 than 6GB
What graphics card you got? A 500w should serve your purpose with head room.