Positioning of the ventilation system, installation of air inlets/outlets

Sensible?

Not really. Either all or nothing.

Is that a disadvantage?

No, it just has to be calculated and the device must be designed/selected accordingly.

In which cardinal direction are the supply and exhaust air mounted on the exterior wall of the house?

That depends on the moon phase. :D Just kidding, since we mostly have westerly winds here in Central Europe, it makes sense to position the fresh air intake to the west and the exhaust air to the north/south/east. Or conversely, exhaust air to the east and fresh air to the north/south/west. Allegedly, there are also functional combination covers that allow both vents on one wall without causing any problems.

Our controlled residential ventilation system is located in the basement, the supply/exhaust air opening is on the upper floor. A shaft is needed for the pipes, but you will need that anyway for the ventilation ducts coming from the ceiling on the ground floor and upper floor.

Not really. Either all or nothing.

And why? According to Selfio, it doesn't matter...

Not connecting the basement is nonsense … do you want to keep going down there to ventilate manually? Is the basement within the thermal envelope? Then connect it.

The problem is the

And why? According to Selfio, it doesn’t matter...

Air and temperature exchange. Also, the system is usually set to slight overpressure. But that is not possible if the overpressure is immediately equalized.

Ok. Then don't I have a problem with condensation there? The basement is not heated!