Sounds like a great trip!
2D I'm not sure about that
if one is in an aircraft not registered in a Schengen country. Can you identify which part of the
SIA site refers?
Had a little problem with our French cousins a year or two ago about this...they insisted (politely) that when going France to Spain in my G-reg, I clear in and out via customs fields.
Hiring a car one day (due to the weather), however, there were no border controls whatsoever!