I'd go for a Coolermaster Elite case, much revered, plenty of space for your needs and a lot easier on the wallet.
Current benches state the 4870 outperforms the 5770 on the whole, but drivers may change that soon. The 5770 has way more feature, being a more up to date card, as you know. Just letting you know.
Also a note, I know you need a gaming PC but a gaming mouse isn't required, as such. Just thinking value minded here, a good laser mouse is great for FPS, RTS and... whatever really. I when this path and can't really fault it.
http://www.overclockers.co.uk/showproduct.php?prodid=KB-102-LG&groupid=702&catid=23&subcat=3
This is the mouse I have (bought it OEM) and it's crisp and accurate.
I'm don't know much of keyboards but I know Saitek are good, so I won't bother suggesting much else (I must say it looks like the Logitech Dinovo Edge though!). Good brands = good keyboards.
Apologies I can't offer advice on the motherboard and CPU, I'm not well-learned on AMD processors as of late. (Though I know the low end Core2Duos clock fiercely without much need for extra cooling. But I believe that's just hassle, and probably money, than you don't want to use.)