Cases are a personal thing. Get one you love, and spend more if you have to.
You will be looking at it every day. Anything with two 120mm intake or exhaust fans will do the job for cooling.
A perennial favorite is the Antec 300 illusion for $70 with free shipping 2600+ buyers can't be too wrong:http://www.newegg.com/Product/Product.aspx?Item=N82E16811129066
Ram and overclocking take a minimal extra out of a psu. It is the graphics that is the big variable.
For most users, a GTX560Ti needs 500w with 30a on the 12v rails plus two 6-pin PCI-E power leads.
It is not wrong to overprovision a bit with 650w or so.