It seems that sparking can be minimized using capacitators on the switches, as seen in this video. Too bad I didn't knew this when I placed the last order from Marco's! I could probably find a similar component locally that could be used instead of this (yellow wrapper 2.2 uF @ 250 volt axial lead non-polarized metalized polyester capacitor).
But I've probably missed a lot more stuff, so I'll chalk this down for ordering later anyway. Right know I also need plastic inlays, rollover switches, foam paddings, LED-holders and a lot more I don't know about at this moment.
I guess that's one of the problems by learning-as-you-go!