I can answer some of your questions, I agree with @T9b you are out of luck with BTC and should try some Alt Coins that you can mine with a number of different Algorithms: Litecoin and Dogecoin (Scrypt), or Darkcoin (X11).
For optimal parameters to mine a Scrypt coin I suggest you try this comparison which is pretty detailed and has most of the GPUs out there:
Temperatures looks more than fine at 68C, I had a few R9 280 and was struggling to keep them below 80C.
If factory overclocked there is not much else you need to do. I suggest you run the Asus Utilities that came with your card to monitor temps, fan speed, etc. Make sure there is enough air circulating within your PC case.
If you mine with your card 24/7 it will fail rest assured, predicting when it's a bit more difficult as it depends on the card components and build quality. Your card is factory overclocked so it will be even more prone to failure if constantly run for mining purposes. I would say a year max, but then some cards fail after 2 weeks or 3 months, etc...
Test it out and make your own judgement, I personally don't think your card will earn you much with mining. That doesn't mean you can't try it out and have some fun with it, you may learn a few things while doing that. ;)