1) Not a whole lot. The numbers are the number of clock cycles it takes for the RAM to respond. From 8 to 7 is like overclocking the RAM by a couple hundred MHz. You probably won't notice the different.
2) Antec 900 and Corsair TX650.
3) Not really, but just get the SATA version, it's like, an additional $4? Anyway you won't see a difference because IDE can transport up to 100 MB/s and a CD or DVD can only transfer a few Megabytes per second, Maximum.
4) You could, or you could be like me. I left the i7 at standard clocks, and raised the memory multiplier from the standard 8x to 12x (20 seconds to do) and my RAM went up from 1066 to 1600 MHz. I never noticed a difference. The i7 technically only supports 800 and 1066 MHz memory, not even 1333. But if you were to leave the multiplier where it is, then it would be useful for overclocking. For example, if you have 1600 MHz ram and you overclock your i7 from 20x133 MHz to 20x200 MHz, then your RAM speed will go from 1066 MHz to ~1603 MHz. Therefore you're still safe on the RAM, which you wouldn't be with the standard 1066 MHz RAM.
I double checked the motherboard I listed. I found it only support Memory Standard DDR3 2200/1333/1066/800. Does it mean I can not use DDR3 1600? If so, maybe I should go with ASUS P6X58D Premium LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 ATX Intel Motherboard http://www.newegg.com/Product/Product.aspx?Item=N82E168...