matboe do you have any suggestion how small/thin I can make them?
As thin as you can, really. The thinner the pads, the higher the spatial resolution. Cables are themselves part of the sensing surface, so the longer the wire the larger the baseline capacitance of the pad. However, as long as the cables are tidied up and taped or otherwise locked in place, this shouldn't be a problem, as long as you use DIFF mode and the prescaler is appropriate.