Wanted to add a fast SSD drive to an old iMac without removing existing HDD or optical
The repair went fine. It's a bit tedious (thanks Apple) but not crazy.
The screws holding the monitor in place are a pain to put back in due to the strong magnets nearby. Hold each screw tightly with a pair of needle-nose pliers while you get them started in their positions and you'll hopefully avoid some wasted time.
I'm not 100% sure but I think it would be possible to avoid disconnecting some of the cables attached to the main board. You really only need to lever the top of the main board forward a little way to get the SATA cable positioned. So I think you can get away without disconnecting the cables along the bottom (power button, IO and a bunch of others.) If I were doing it again I'd try to get away with that.
Instead of disconnecting the antennae cables from the AirPort card, just unplug the airport card itself. That is quicker (only one little screw) and avoids the risk of damaging those critical cables.