That shouldn't be a problem, there are a couple of videos about the installation on Youtube, and it would certainly increase your performance in the iMac.

Yes, you can do this!
However, since the fan will then spin up due to the deviating hard disk firmware, the installation of the free programme "SSD Fan Control" is required! Select "SMART" in the programme and that's it. The temperature is then read out via the S.M.A.R.T. values of the hard disk!