Even on 1), the first day of the week being Sunday (US) and Monday (Europe) screws me up constantly, as someone who is in both worlds now.

I often pick the wrong date for meetings because I'm assuming next Monday will be in the first column, not the second. As dumb and simple as it is, when something has been drilled into you since about age 3 its tough to get in the habit of double checking it when it starts becoming inconsistent.