What's needed to upgrade storage on iMac 17,1 with SSD configuration?

The SSD that is currently installed in your computer is a blade drive installed in the slot on the backside of the main logic board. To install an additional 2.5-inch SATA SSD, you will need to de-adhere the display carefully, remove the logic board, install the appropriate SATA cable, route the SATA cable and reinstall the logic board, install the appropriate mounting hardware for the 2.5-inch SSD, install the 2.5-inch SSD, then reinstall the display using adhesive tape. The SATA cables for these machines should be able to handle the temperature (I've never noticed any problems after installing 2.5-inch SSDs and have never needed a third-party temperature sensor for these models). Hope that helps!