What external devices can be connected to the 2nd Gen dongle?

I just got the 2nd generation AutoPi dongle and so far it works. What accessories work with this thing? I see a lot of external things being connected to the DIY version, can I get a touchscreen connected to it? Can there be a connection made to a Pioneer (4200NEX) head unit. I would love to display the graphs and the gauges to show performance data, etc.

If this has been asked before, please link me to posts or tutorials.