i3 is dual core. i5 is quad core. i7 is quad-core but as far as I know it has a double-threading, something like that, technology so each core is basically 2 cores in some way. i7-970 and i7-980X are hexa-cores but I think they also have double threading so it comes to 12 cores in the end.
If you're willing to pay more cash, the GTX 460 is a good card. But if you're not, the HD radeon 5770 which BiGyLiLuPdAmIdL posted is the best one.
After a little googling it seems that Rosewill isn't very good in PSU's making. I advise you to wait for some experts ideas on another PSU but I think this one is good, wait for confirmation though : Newegg.com - Antec TruePower New TP-750 750W Continuous Power ATX12V V2.3 / EPS12V V2.91 SLI Certified CrossFire Ready 80 PLUS BRONZE Certified Active PFC "compatible with Core i7/Core i5" Power Supply
- 84.99$ after rebates ( expensive yet reliable and trusty
, but possibly you can go cheaper as I'm almost sure your PC wouldn't need that amount of power. But a 750W will give big room for possible future upgrades )
When you said got processor and mobo, you mean you bought and received them? I didn't understand
I apologize to you because I won't be able to reply to you for the next 7 days as I have some stuff I need to do. So you can expect help from other people. Sorry, hope I helped till now.