CPU - Intel Core i5 2500k - yes
Motherboard - P67 or Z68 - Yes. Both good boards.
GPU - Geforce 560Ti or 570 - Radeon 6870 or 6950 anyone of these cards is fine.
PSU - Get a decent 500W minimum.
HDD - Split your hard-drive in two,so you have 2 x 1TB hard-drives which means one will back up the other. If you have everything on the one drive and it fails then you could lose everything.
Get a decent case, a gaming PC produces a fair bit of heat so keeping the insides cool is a must.
If you want I'll put together a spec for you tomorrow and you can run it by your cousin. I have been building a while now and I like my FPS's .
Let me know.