Dying iMac drive, emergency repair assistance [on hold]

I have a older 27" iMac ( 2011 ) and the hard drive is on its way out in a serious manner, ( smart status failing, io error every few seconds in much kernel log , speed of io is the worst I have ever seen) out of AppleCare, cannot get it to a apple store for at least a week due to them being busy and I require the machine for tomorrow . I am wondering if anyone can fill me in on a few questions. I will be starting this task in about 8 hours

1. Can I ignore the temperature sensor if I install any sata drive in it or will it cause long term damage ? Can I hack it up with something else ?? ( if so what are the pinouts to the sensor ) can I cheat by finding a FireWire drive and simply install/ boot from that temporarily ? Would it be smarter to get my hands on a 128 gig sdhc card and use that instead ?


2. Is it possible to create a bootable flash drive to re-install mountain lion, and can I do so from any old OS X machine ( yes I know , but i have no reason to slow down a ancient machine any more by installing Yosemite ) if not is it possible for me to use dd to copy the recovery partition from another iMac to the new drive ? Or is it locked to the hardware serial number of a specific iMac ?


3. Is it really "that awkward" to replace the drive ? ( I read a few guides they are all full of comments of people complaining about it being a very fiddley job, I have a little bit of electronics experience ( 10+ years of hobby electronics , 13 years of professional software development with over half of it being embedded systems )


4. Has anybody ever done this ( and if so how long did it take ) ?
   
   
   
   5. What is my risk of bricking the machine or damaging a ribbon cable which I cannot easily replace?
   
   
   6. Any maintenance that I should perform while I am In there ?
   
   
   
   

P.s. If this question is considered to broad please feel free to edit it to narrow its scope rather than vote to close