1) I would try to get a GTX 680 in there! So I second a lower spec motherborad and smaller PSU. Z77 boards are out so you could grab a $150 ASUS P8Z77-V LK (SLI) (again might be overkill) or even a $110 GIGABYTE GA-Z77-DS3H (might need a sound card with this one), pair it with the i5-3570K which will be out in two weeks. The computing gains are not as impressive when it come to games, but the savings on power are. Your PSU requirements won't Exceed 300W total so get a 550W, or a 650W for overclocking, 750W for SLI, 850W for SLI and overclocking.
2) Your system will barely tap 8GB of RAM so 16GB is overkill. LGA 1155 is dual channel not quad. Check out the review of this kit and join the club, be warned that other kits will look like kids play:
Samsung 30 nm Green PC3-12800 Low Profile 1.35 V DDR3 Review - Page 8/8 | techPowerUp
That's more than $130 worth of saving and a reason to go for the GTX 680. Next investment should be SSD, then better input (Keyboard, Mouse, gamepads) and output (3D monitor, headset, speakers) and so on.
3) for cooling and case: it's all relative (as is all parts of your build). If you go for a large case, then you will need a large heatsink. The CM Hyper 212 Evo will create nice and quite airflow in amid-tower case, but won't be as efficient in a larger case. HAF's are all great and probably the best to build with and last a long time, but as Funguseater said two fans are not enough for a rig with a video card. I prefer the quietness and airflow of Rosewill cases, especially the mid-tower Blackhawk becasue it has quite fans in the right places. 2 at the front, one at the side, rear and top, and the size is right. 140mm.