Intel Mac :: Replace Hard-drive Before Taking It For Service

I have some complex questions regarding an iMac, a Time-Machine backup, and iTunes on an iPod. I live about halfway up an extinct volcano about 12 miles north of San Jose Costa Rica. Some months ago, we had a thunderstorm and as I reached to unplug my computers lightening struck about 50 meters from my house. I had an iMac with a 3-Tb external backup drive, a PC laptop and a laser printer on the same power strip.There was a definite surge and the light brighten and then power was lost for a few minutes.When power was restored, the PC and the laser printer seemed to work fine but the iMac was cold.Is is possible that the power supply was fried and not other essential parts? Would it be worthwhile to replace the power supply? Can I, with limited experience and tools do it or need I take it to a technician? My concern is that if the hard-drive is good, there is personal information on it that I don't want to risk.Do I need to replace the hard-drive before taking it for service? How hard is that, can I do it? I have seen videos of the drive replacement on-line.If there is a saving grace with this it is that the Time-Machine backup seems fine although I have only accessed the data through Finder.I replaced the iMac with a Macbook Air with significantly less mass storage and I can't just move files to the Macbook. My problem is that I have an iTunes library of some 10,000 songs on the backup and until recently on a 160 Gb iPod which was old and it crashed.I have replaced the iPod but have not tried to restore the iTunes library to it because of my confusion about how to do that.Can anyone tell me how I might do that or give me any insight into the process?

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iMac