People have been doing this for a long while, and it is pretty straight forward.
The existing cables will work without issue.
The only thing that you need is a SATA 3.5" to 2.5" adapter bracket or caddy, this can be purchased for less than $10 on ebay or Amazon.
You could also get an external temperature sensor SATA adapter. These tend to be less than $40, and sometimes you can find them for cheaper. It isn't required, as there are other solutions, such as SW, shorting the temp sensor wire pins, or adding your own temp sensor.
I suggest just getting the SATA adapter, as you do it once, and you never need to worry about it again. It also will give the OS accurate temp readings and adjust the fan speeds accordingly.
Here is the SATA temp sensor adapter cable by OWC:
OWC's in-line solution is the only hardware digital thermal sensor on the market allowing a third-party SATA drive to be installed in your iMac.
www.amazon.com
That link also included the tool kit, which is just a little more, and would probably be worth to get it if you do not have one already.
Here is a bunch of brackets:
Amazon.com: 2.5 to 3.5 adapter
www.amazon.com
Some people even just use double face tape, but the adapters are so cheap, you might as well just do it right.