Howdy,.
1. For gaming and general use, you really don't need an i7 honestly. The difference between i5s and i7s is a feature called HyperThreading. HyperThreading basically allows the CPU to "pretend" to have twice the cores it actually has. For example an i7 3770K will be 4 physical cores 8 threads. This has an advantage if you were to get into heavy video editing, media encoding, CAD design, etc, as these are CPU intensive workloads that can benefit. However, there is no game on the market today, or in the future that will ever use HT. So unless you're planning on doing a lot of heavy productivity work, then the i7 really is just going to cost you more for nothing. Even occasional productivity work, the i5 is still good enough.
AS far as what the difference with the letter designations, the S means its a low power vairant, for a powerful desktop machine, those won't be particularly appealing. The K model number indicates an unlocked multiplier, this will bear particular importance for overclocking, basically the K means, you can overclock that model. If it has no K or S at the end of the model number it means the multiplier is locked, and it is not a low power model.
2. The difference between GDDR3 and DDR3 is GDDR3 is video RAM, which will be found in video cards. The most current version of video RAM is GDDR5, any decent video card you will be considering will have it. As far as RAM for the computer itself, honeslty 16GB is overkill. Take it from me, I'm a multitasking nut, and try as I might, I've never managed to use 8GB in Windows Task Manager, let alone 16GB. 8GB would be plenty, as far as specific brands, all them are good really. Gskill, Corsair, Kingston, Samsung, PNY, etc. I would suggest buying RAM that is 1.5volts however, some of Kingstons are 1.65v. Intel CPUs like 1.5v better from what i've heard.
3. The Asus board you're looking at is pretty nice. I'm personally not a big fan of Gigabyte boards, only because I had a bad experience with one. Thats not to say that those models you're looking at would be bad choices. I would say if you're willing to spend the cash (perhaps with the money you save going with an i5) Asus Sabertooths are awesome motherboards, with 5 year warranty. But the Intel ones do cost a pretty penny.
Full Price
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Open Box Deal- (Asus will honor the warranty)
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
4. I don't have any experience with RAID configurations myself either, so I'll defer to someone else's knowledge.
5. CoolerMaster 212 Evos would be my answer.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
6. What video card are you considering? I'd say the best on the market right now is the GTX 670 (680s cost more and really aren't worth the extra performance for the price difference), there are cheaper options on the market that are pretty good too for a single card rig. I guess we have to talk about that one more.
As far as a PSU, I would consider this one to be of very high quality, with more than enough power for the system.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...