+1 on the Alienware, though this time i chose to hunt for a case and build my own.
I found a Area-51 ALX (best OEM case ever IMHO) 5 months ago and bought my Sandy Bridge parts myself, found a nice CPU+mobo+RAM+GPU combo before it arrived. Very happy with everything.
If you didn't power your motherboard since it broke, you'll be fine after you change it with a same spec'd one (for piece of mind). Luckly you were able to read the specs, I did it plenty of times on mobos and GPUs over the years and I can tell you it sucks not having the values.
If you know...
There's no such thing as enough power :D.
Seriously though, a 560Ti would be enough, heck, great, but if you can drop the little extra on the 570, why not. Anyway, you'll be happy with either of them.
Cheers
Those temps are fine, but of course there's always room for improvement.
Review your case airflow and definitely add at least one intake fan, as said above, you'd want one with high CFM and low noise (dB). I'm personally kind of a Scythe fanboy, they usually have a great CFM:dB ratio.
Cheers
No problems here, as per MSE and Kaspersky.
Scan your whole system with a free online scanner like bitdefender or Kaspersky to make sure it hasn't spread.