Passengers in Denmark are trained to look before opening the door (by parents, usually), and it's the drivers responsibility if the passenger isn't capable of that.
A taxi driver will often remind you at the end of the journey, if you're obviously foreign.
(And you have forgotten passengers in the back seats.)
There are now some protected bike lanes in which parked cars provide part of the protection (!), but you need a lot of space in order to construct one without having the passenger-side door zone overlapping the protected lane.
It's pretty nice as a cyclist, in the minority of cases where there was enough space to do it this way. I suspect it may have required eliminating an entire traffic lane in some places!
No, it's on the right (i.e. correct) side of the car - drivers are trained to look into the side mirror before opening the door, passengers not (and even if they were, they can't use the mirror on their side).