When Maria is singing "I Have Confidence" she comes up to the front of the house and it shows that there are several large windows by the front door but for the rest of the movie there are no large windows next to the door.
Can I suggest you watch it again! In the film it is obvious that there is a sort of hallway between the front door and the top of the stairs the depth it is makes it entirely possible for there to be rooms which we don't see to accommodate the windows on the outside wall that you are referring to.
If you notice in this scene she hoes into a yellow house, the same one seen in the escape scene pushing car out the gate. The terrace scene as well as the boat scene show a white house - actually two different palaces in Salzburg were used in filming and the interior was a set. The only interior scene showing a room in one of these palaces was the Venetian room copied on a set from the white palace of Leopoldskron.
Many of these original settings were also seen again 25 years later in the "Sound of Christmas" special with Julie Andrews revisiting Salzburg.
For over 20 years I was the guide on the Sound of Music Tour in Salzburg.
Can I still suggest that you watch it again, the fact that it was filmed in two different locations (ok 3 if you count the Hollyood set) is irrelevant given the size of the hall/vestibule area next to the door it would be an even bigger mistake if the windows were there!