I used a T4 Torx driver to remove these screws on mine (I didn't have a T3 handy). Note that there are springs behind the copper plate directly underneath the Torx screws. Be careful not to lose these.

All of these connectors have a backflip mechanism (a bar is flipped up to allow insertion or removal of the ribbon cable) except the smallest two. One is pictured in this photo second from left on top, and the other is hidden on the top underneath other cables. These two connectors have no locking mechanism. The cable is simply pulled directly out.

Agree with the comments above. The screw pictured in Step 9 is behind the rubber thumb rest in step 8 and must be removed before the back can be taken off. Also, the buttons are attached to the back plate by a screw, so will come off with the back plate. They are attached to the motherboard with a ribbon cable that must be disconnected.