Yesterday I finished preparing the 7 touch pads and started putting together the cables that connect them to the MPR121 breakout boards.
One of the mistakes I have made is ordering the wrong magnetic tape. The one I've received isn't self adhesive and it has striped polarity north-south which makes it harder for both parts to snap in the right position. This has made things longer and is something I will have to change for the next prototype.
Another problem I have encountered is the fragility of the copper tracks where I have soldered the cable to. In fact, the first time round they snapped with a little pull. I managed to sort this out, but I am definitely worried about the durability of this so I will have to give it some thought to try and come up with a better solution. However, I tested the continuity with a multimeter and everything seems OK for now so I will stick to this for now.
As I type this, I have received the clear vinyl to protect the electrodes and some cute rubber feet. The vinyl feels quite smooth, which is a relief as I recalled these matte translucent ones to be quite rough.