This post is a follow up on the exterior door handles. I agree with those above who said it is natural to use one's left hand on the driver's side door handles and the right hand on the passenger side door handles. However, on many (perhaps most) cars including the model S, it doesn't matter that much. On an S, you just need to pull the handle out a little, it activates the electronic opener and the door opens a bit. One can easily do this one-handed or even one-fingered using either hand.
Door opening is not as straight forward on the 3. One cannot open the door with one finger (or at least I don't know how). To open it one-handed, there are two parts to the process -- a push with the correct thumb and a pull with the remaining fingers. Of course, as the owner, you'll quickly get used to the routine. But some people who approach the car for the first time are befuddled -- thus the occasional need to instruct or demonstrate. Again, not a huge deal -- but certainly a personality quirk of model 3.