Are the needed libraries already in the geexbox distribution (RPi.GPIO)?
At the moment we don’t supply any RPi-specific libaries.
Do you have any suggestions for a touchscreen which can work directly with Geexbox?
No idea. A while ago someone asked for tslib. We did add it as optional package but never got any feedback…
a modified skin to show the needed controls and a touchscreen
XBMC already has a skin for such devices. It’s named “touched”. Currently we don’t build it by default, but I guess it can be installed the same way as any other skin.
BTW, isn’t XBMC a bit heavy to be used just as an audio player ? Even though I can’t suggest one, I could imagine that there are alternatives…