On the intel build. I would move up to the Pro series 840 TLC isn't a strong flash over time the MLC flash of the 840 Pro will prove to have longer lasting performance over time.
Also, unless you have specific audio needs I would stick to your onboard audio. Reason being is unless you are using anything with a s/pdif connnection or RCA then it would make sense otherwise the onboard has enough.
In terms of memory I'd say you are fine you can always in the future purchase more I'd say 16 would be a good spot for you. And beyond 16 you would need pro of ultimate of windows 7 assuming that is what you have.
I would say the same sorts of things I see you went with the 660ti which is a stronger card however I still feel the intel build is stronger. And in terms of cases that is a personal choice on your part I would get the fractal design define r4 because I feel like you get a lot of premium case design for a fraction of the price plus it looks really classy and clean but again I'm not you